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THE  GROSS  AND  MINUTE 
ANATOMY  OF  THE  CENTRAL 
NERVOUS  SYSTEM 


GORDINIER 


THE  GROSS  AND  MINUTE 
ANATOMY  OF  THE  CENTRAL 
NERVOUS  SYSTEM 


H.   C.   GORDINIER,  A.M.,  M.D. 

PROFESSOR     OF     PHYSIOLOGY     AND     OF     THE     ANATOMY    OF    THE     NERVOUS     SYSTEM     IN     THE 
ALBANY  MEDICAL  COLLEGE;    MEMBER  AMERICAN  NEUROLOGICAL  ASSOCIATION 


Mitb  48  jfulUpage  plates  ant)  213  ©tber  Ullustrations 

MANY    OF    WHICH    ARE     PRINTED     IN    COLORS,    A 
LARGE  NUMBER  BEING   FROM  ORIGINAL  SOURCES 


PHILADELPHIA 

P.    BLAKISTON'S    SON    &    CO. 

I0I2     WALNUT     STREET 
I  899 


Copyright,  1899,  by  P.  Blakiston's  Son  &  Co. 


Press  of  Wm.  F.  Fell  &  Co^ 
1220-24  Sansom  St., 

PHILADfLOHl*. 


TO 

professor  /ift.  alien  Starr, 

IN    GRATEFUL    ACKNOWLEDGMENT    OF    MANY    KINDNESSES, 

THIS    BOOK    IS    SINCERELY    DEDICATED    BY 

ONE    OF    HIS    FORMER    PUPILS. 


347564 


PREFACE. 


The  absence  of  a  complete  work  in  English  on  the  Anatomy 
of  the  Central  Nervous  System  has  convinced  the  author  of  the 
necessity  for  the  preparation  of  a  systematic  text-book  which  shall 
present  this  most  difficult  subject  in  a  concise  but  comprehensive 
manner — a  book  that  will  meet  the  needs  of  medical  students 
and  at  the  same  time  be  of  service  to  the  clinician  in  associ- 
ating symptoms  of  nervous  diseases  with  anatomic  facts.  This 
work  consists  essentially  of  the  lectures  which  the  author  has 
been  accustomed  to  deliver  to  his  students,  amplified,  rearranged, 
and  illustrated  with  many  cuts,  both  original  and  borrowed. 
The  writer  desires  to  acknowledge  his  indebtedness  to  the 
magnificent  works  of  Cajal,  Edinger,  Flatau,  Dejerine,  His, 
Jakob,  Koelliker,  Lenhossek,  Quain,  Retzius,  Starr,  Van  Gehuch- 
ten,  Wernicke,  and  others. 

It  is  a  pleasurable  duty  to  testify  to  the  help  in  this  work  from 
the  interest  of  many  pupils  and  from  the  investigations  set  on 
foot  by  the  intelligent  questions  of  many  of  those  young  seekers 
after  truth  in  successive  years.  With  the  earnest  hope  that  the 
author's  labors  will  be  helpful  to  some,  and  may  perhaps  clear 
up  some  obscure  questions  here  and  there,  this  work  is  sub- 
mitted to  the  students  of  medicine. 

The  writer  owes  a  debt  of  gratitude  to  his  former  students, 
Drs.  James  T.  McKenna  and  Edgar  R.  Stillman,  for  assistance 
rendered  in  the  preparation  of  this  work,  and  to  Mr.  E.  N. 
Reed  for  assistance  in  reading  proof-sheets  ;  to  Wait  H.  Still- 
man  and  Joseph  McKay,  of  Troy,  N.  Y.,  for  the  preparation 
of  photographs  and  microphotographs,  and  to  Dr.  Thomas  W. 
Salmon  for  the  execution  of  several  of  the  original  drawings. 

Hermon  C.  Gordinier. 

Troy,  N.  Y.,  June  2,  i8gg. 


CONTENTS. 


CHAPTER    I.  Page 

The  Histologic  Elements  of  the  Nervous  System, 17 

Histology  of  the  Nerve-cell, 17 

Forms  or  Varieties  of  Nerve-cells, 24 

Purkinje  Cell, 25 

The  Basket  Cell  of  the  Cerebellum, 28 

Pyramidal  Cells  of  the  Cortex, 28 

Cell-processes  and  Nerve-fibers, 30 

The  Axis-cylinder, 31 

Nerve-fibers, 31 

Non-medullated  Fibers, 35 

The  Peripheral  Nerve  Terminations, 37 

The  Terminations  of  Sensory  Nerves, 38 

The  End  Bulbs  of  Krause, 40 

The  Tactile  Menisques, 42 

The  Corpuscles  of  Golgi, 43 

The  Muscle  Spindle, 43 

The  Terminations  of  the  Motor  Nerves, 45 

Neurone  or  Neurodendron, .        .    .  47 

The  Neuraxone  or  Axone, 49 

The  Neuroglia, 52 

Blood-vessels  and  Lymphatics, ....  58 

The  Tunica  Adventitia, 5^ 

Tunica  Media, 59 

Tunica  Intima, 59 

Veins,      .    .    .    .    ^ 60 

Capillaries, 60 

Lymphatics, 61 

The  Adventitial  Lymph-space, 63 

Pericellular  Lymph -spaces,  ....             63 

CHAPTER  n. 

Spinal  Cord, 64 

The  Nerve-cells  of  the  Cord, 76 

The  Course,  of  Fibers  in  the  Sensory  Tracts  of  the  Cord, 95 

The  Course  of  the  Fibers  of  the  Dorsal  Funiculi  or  Posterior  Columns,   .    .  97 

The  Column  of  Goll, 99 

The  Columns  of  Burdach, 99 

The  Cornu  Commissural  and  Septomarginal  Descending  Tracts, loo 

The  Cornu  Commissural  Tract, loi 

The  Septomarginal  Tract, 102 

Gowers'   Anterolateral  Ascending  Tract — Fasciculus  Ventrolateralis  Super- 

ficialis, 103 

The  Anterolateral  Descending  Tract  of  Marchi  and  Lowenthal, 104 

The  Olivary  Tract  of  Bechterew, 105 

A  Long  Sensory  Tract  in  the  Gray  Matter  (Ciaglinski), 106 

Lissauer's  Tract, 106 

Anterior  Ground  Bundles, 107 

The  Ground  Bundles  of  the  Lateral  Columns,  or  the  Lateral  Limiting  Layers,  107 

The  Spinal  Nerves, 108 

Spinal  Ganglia,      109 

The  Anterior  or  Motor  Nerve-roots, 112 


X  CONTEMS. 

Si'iNAl.  Cord  {Continutd) —  V\i^^ 

The  Posterior  or  Sensory  Nerve-roots, 113 

The  Appearances  of  Transverse  Sections  of  the  Curd  at  Different  Levels,    ....  II4 

Neuroglia  of  the  .Spinal  Cord, 1 1? 

The  Subpial   .Neuroglia  Layer,  the  Kimlenschicht  of  the  (iermans II9 

ro.-iterior  Horns,         122 

The  Suhstaniia  (_;elatinosa  Rolandi, 122 

The  Region  of  the  Central  Canal,  ...             122 

The  Blood-supply  of  the  Spinal  Cord, 122 

Veins  of  .Spinal  Cord, 1 24 

CHAPTER   in. 

The  MEi)fLi..\  Oblong.\ta  or  Bulb, 125 

The  Fourth  Ventricle, *3* 

.'\  Transverse  Section  of  the  Medulla  at  the   Level  of  the  First  Cervical   Nerve.  .  137 

.\  Section  at  the  Level  of  the  Motor  Crossway 140 

The  Raphe, ' 146 

The  Forniatio  Reticularis,     .    .                 146 

Connections  of  the  Hypoglossal  Nuclei, 152 

The  Vagus  and  (ilossopharyngeal  Nerves, 155 

The  Olivary  Bodies, '59 

The  Central  Tegmental  Tracts  of  Bechterew  and  Flechsig, 163 

Section  through  the  Middle  of  the  Olivary  Bodies 163 

.\  Transverse  Section  of  the  Medulla  near  its  Junction  with  the  Pons 166 

The  .'\bducens  Nerve, 166 

The  F"acial  Nerve,          ^68 

Connections  of  the  Facial  Nerve, '7^ 

The  Auditory  Nerve, *7^ 

The  Cochlear  Nerve .    .             .    .  171 

The  Vestibular  Nerve, ....172 

Connections  of  the  Auditory  Nerve 175 

The  Superior  Olivary  Body 17^ 

Connections  of  the  Vestibular  Nerve, .             176 

With  the  Cerebellum, 176 

With  the  Lateral  Fillet 177 

With  the  Internal  or  Mesial  Pallet 177 

With  the  Nuclei  of  the  .Si.\th  Ner%'e, 177 

With  the  Olivary  Body  and  the  Lateral  Column  of  the  Same  Side,     .  177 

The  Pons  Varolii,      .    .                 ....  178 

A  Transverse  Section  of  the  Pons, .  179 

The  Nuclei  of  Origin  of  the  Trigeminal  Nerve, 182 

The  Cerebral  Connections  of  the  Trigeminal  Nerve, 185 

CHAPTER  IV. 

The  Cerebellum  or  Epenceph.\lo.\, i86 

The  Vermis  or  Worm,       '88 

Superior  Surface, 188 

Inferior  Surface,     ...             189 

Lobules  of  the  Su()erior  or  Dorsal  Surface  of  the  Cerebellar  Hemisphere,      ....  190 

Lolmles  of  the  Inferior  Surface  of  the  Cerebellar  Hemisphere, 190 

Minute  Anatomy  of  the  Cerebellum, 193 

The  Cortex  of  the  Cerebellum 198 

The  Cells  of  Purkinje, 200 

The  Cerebellar  Peduncles, 202 

The  Middle  Peduncles, 203 

The  Inferior  Cerebellar  Peduncles,  or  Corpora  Restiformia, 203 

CHAPTER  V. 

The  Recion  of  the  Mid-brain, 210 

The  Corpora  Quadrigemina, 210 

^Iinute  Anatomy, 212 

The  Cerebral  Peduncles 220 

The  Mesial  Fillet,  or  Lemniscus 223 

The  Superior  Cerebellar  Peduncles 229 


CONTENTS.  xi 

The  Region  of  the  Mid-brain  [Continued) —  Page 

The  Superior  Longitudinal  Bundle, 230 

The  Motor  Oculi,  or  Third  Pair  of  Cranial  Nerves,  .    .    .    , 235 

The  Connections  of  the  Oculomotor  Nucleus,. 238 

The  Fourth  Pair  of  Cranial  Nerves, 240 

The  Superior  or  Accessory  Nucleus  of  the  Fifth  or  Trigeminal  Nerve,       240 

CHAPTER  VI. 

Region  of  the  Third  Ventricle, 234 

The  Third  Ventricle, 244 

The  Pineal  Gland,  or  Conarium, 246 

The  Posterior  Commissure, 248 

The  Optic  Thalami, 248 

The  Ganglion  Habenulre, 257 

Connections  of  the  Opiic  Thalamus, 258 

The  Subthalamic  Region,  or  Stratum  Intermedium, 259 

The  Red  or  Tegmental  Nucleus  of  Stilling, 261 

The  Connections  of  the  Red  Nucleus, 262 

The  Substantia  Nigra  (Locus  Niger;  Intercallatum  of  Spitzka),         ....  263 

Retina, 263 

The  Layer  of  Optic  Nerve-fiber*, 264 

The  Layer  of  Ganglionic  Cells, 264 

The  Inner  Molecular  Layer, 265 

The  Inner  Nuclear  Layer, 265 

The  Outer  or  External  Molecular  Layer, 266 

The  Outer  Nuclear  Layer, 266 

The  Layer  of  Rods  and  Cones, 266 

The  Pigment-Layer, 267 

The  Course  of  the  Optic  Nerves  and  Tracts, 268 

The  Connections  of  the  Optic  Tracts, 273 

The  Optic  Chiasm, 274 

The  Pituitary  Body, 276 

The  Tuber  Cinereum, 279 

The  Infundibulum, 279 

CHAPTER  VII. 

The  ISIembranes  of  the  Brain, 280 

Dura  Mater, 280 

Processes  of  the  Cerebral  Dura  ]Mater, 281 

The  Falx  Cerebri,  or  Processus  Falciformis  ]Major, 281 

The  Tentorium  Cerebelli,     .    .             281 

The  Falx  Cerebelli,  or  Processus  Falciformis  Minor, 282 

The  Arachnoid  Membrane,       284 

Subarachnoid  Spaces, .         285 

The  Pacchionian  Glands,  or  the  Arachnoid  Villi, 287 

The  Pia  Mater,               288 

The  Velum  Interpositum  and  Choroid  Plexuses, 288 

The  Tela  Choroidea  Inferior  and  Choroid  Plexuses  of  the  Fourth  Ventricle,  291 

Choroid  Plexuses  of  the  Fourth  Ventric'e, 291 

CHAPTER   VIII. 

Fore-brain  or  Prosencephalon, 293 

Fissures, 294 

The  Fissures  of  the  External  Surface  of  Each  Hemisphere,    .......  294 

The  Longitudinal  Fissure, 294 

The  Transverse  Fissure, 294 

The  Fissure  of  Sylvius, 298 

The  Fissure  of  Rolando,       299 

The  Parieto-occipital  Fissure,      299 

The  Intraparietal  or  Interparietal  Fissure, 300 

The  Calcarine  Fissure, 3°° 

The  Collateral  Fissure,      . 3°*^ 

The  Callosomarginal  Fissure, 3^3 


xii  CONTENTS. 

FoRE-iiRAiN  OR  Prosenckphalon  {Continue J) —  I'ale 

The  Convolutions,  Ciyri,  or  Lobules, 303 

The  Frontal  Lohe ^703 

The  Parietal  Fobe, -506 

The  Ascending  Parietal  or  Posterior  Central  Gyrus,     ......  306 

The  Superior  Parietal  Convolution 307 

The  Inferior  Parietal  Convolution,           308 

The  Occipital  Lobe, ^oS 

The  Occipital  Convolutions, 309 

The  Insula,  or  Island  of  Reil, ^lo 

The  Temporosphenoid  Lobe,       313 

The  First  or  Superior  Temjioral  Convcilution, 313 

The  .Second  or  Middle  Temporal  Convolution,      .    .    .    .   - 314 

The  Third  or  Inferior  Temporal  Convohitioii, 314 

Convolutions  of  the  Mesial  -Surface, 315 

The  Marginal  Convolution, 215 

The  Gyrus  Fornicatus,      316 

The  Quadrate  Lobe,  or  Precuneus, 316 

The  C'uneus, ji6 

The  Lingual  Lobule, jl6 

The  Limbic  or  Falciform  Lobe, ^17 

The  Gyrus  Hippocampus,  or  Subiculum  Cornu  Ammonis, 317 

The  Dentate  G)  rus,  or  Fascia  Dentata,      318 

The  Base  of  the  Cerebral  Heniisi)heres, 318 

The  Inferior  Longitudinal  Fissure, 319 

The  Olfactory  Pulb, 319 

The  Olfactory  Tract, 319 

The  Corpus  Callosum, 319 

The  Anterior  Perforated  .Spaces, 320 

The  Sylvian  Fissure, 320 

The  Optic  Chiasm  or  Decussation 320 

The  Interpeduncular  Space, 323 

The  Tuber  Cinereum 32  5 

The  Infundibulum,  .    .         323 

The  Pituitary  Pody,  or  Hypophysis  Cerebri,     . 323 

The  Corpora  Albicantia  or  Mammillaria, 324 

Posterior  Perforated  Space, 324 

The  Crura  Cerebri,  or  Peduncles  of  the  Cerebrum, 325 

Olfactory  Lobe,  Bulb,  Nerves,  and  Tracts, 326 

The  Olfactory  Nerves, 326 

Olfactory  lUilb  :   Its  Minute  Anatomy, 328 

The  Outer  Layer,  or  Layer  of  Olfactory  Nerve-fibers,  .    .    .    .  328 
The  Layer  of  Olfactory  Glomeruli ;  the  Stratum  Glomerulo- 

rum, 329 

The  Molecular  Layer,  or  Stratum  Gelatinosum 330 

The  Layer  of  Central  Nerve-fibers, 332 

The  Olfactory  Tracts, 332 

The  Trigonum  Olfactorium  and  Space  of  Broca, 335 

The  Anterior  Commissure, 336 

CHAPTER  IX. 

Histology  of  the  Cerebral  Cortex,  together  with    the   Minute  Anatomy 

OF  THE  Centrum  Ovale, ........  338 

The  Histology  of  the  Cerebral  Cortex, 338 

Layers  of  Cortical  Cells  and  Fibers, ' ^43 

Superficial,  Molecular,  or  Outer  Cortical  Layer, 343 

Layer  of  Small  Pyramidal  Cells, 345 

Layer  of  Large  Pyramidal  Cells, 346 

Layer  of  Polymorphous  Cells, 350 

The  Anatomy  of   the  Cornu  Ammonis,  or   Hippocampus    Major,  and    the  Gyrus 

Dentatus, 350 

Gyrus  or  Fascia  Dentata,      359 

The  Centrum  Ovale, 362 

The  Association  Fibers, 364 

Fibrae  Arcuatas  Propriae, 364 


CONTENTS.  xiii 

Histology  of  the  Cerebral  Cortex,  together  with  the  Minute  Anatomy  page 
OF  the  Centrum  Ovale  {Contimied) — 

The  Cingulum,  or  Bundle  of  the  Gyrus  Fornicatus, 364 

The  Fasciculus  Arcuatus, 364 

The  Fasciculus  Uncinatus, 368 

The  Superior  Longitudinal  Fasciculus,  or  Fasciculus  Arcuatus  of  Burdach,    368 

The  Inferior  Longitudinal   Bundle, 368 

Fasciculus  Occipitofrontalis  (Forel  and  Onufrowicz), 369 

The  Perpendicular  Fasciculus  of  "Wernicke, 370 

The  Projection. System  of  Fibers, 373 

CHAPTER  X. 

General  Anatomy  of  the  Interior  of  the  Cerebral  Hemisphere, 387 

Corpus  Callosum, ogy 

The  Lateral  Ventricles, 303 

Eminentia  Collateralis, 394 

The  Corpora  Striata, 308 

The  Lenticular  Loop,  or  Ansa  Lenticularis,      402 

The  Tractus  Striothalamicus  (Edinger),     . 403 

The  Taenia  Semicircularis, 404 

The  Internal  Capsule, 407 

The  Fornix, , 413 

The  Septum  Lucidum,       414 

The  Fifth  Ventricle,          ^    !.'!'.!!  414 

CHAPTER  XI. 

The  Blood-vessels  of  the  Brain, 416 

Carotid  Arteries, 418 

The  Anterior  Cerebral  Arteries, 421 

The  Middle  Cerebral  or  Sylvian  Artery, 422 

The  Central  or  Ganglionic  Branches  of  the  Middle  Cerebral,     .    .    .  423 

Posterior  Communicating  Artery, 424 

The  Anterior  Choroid  Artery, 424 

The  Vertebral  Arteries, 425 

The  Basilar  Artery, * 425 

The  Posterior  Cerebral  Arteries, 425 

The  Circle  of  Willis, 428 

Blood-vessels  of  the  Cerebellum, 430 

Arterial  Supply  to  the  Pons  Varolii  and  Medulla  Oblongata, 432 

The  Venous  Systems  of  the  Brain,      435 

Characteristics  of  the  Veins  and  the  Venous  Circulation,      435 


The  Cerebral  Veins, 


435 


The  Superficial  Veins, 436 

The  Deep  Cerebral  Veins, 440 

Veins  of  the  Cerebellum, 440 

The  Venous  Sinuses, 442 

The  Emissary  Veins, 447 

CHAPTER  XII. 

Cerebral  Localization, 448 

The  Cortical  Centers  for  General  Sensations, 454 

The  Centers  of  Vision, 457 

Retinal  Representation  in  the  Occipital  Cortex, 462 

Color-vision,   .    , 462 

The  Auditory  Centers, 462 

The  Centers  for  Language, 465 

The  Center  for  the  Reception  of  Heard  Words,        466 

The  Center  for  the  Reception  of  Memories  of  the  Appearance   of  Objects 

Seen  and  for  the  Appearance  of  Words  as  Written  or  Printed,    .....  469 
The  Center  for  the  Reception  of  the  Appearance  of  Objects  Gained  through 

the  Sense  of  Touch, 470 

The  Motor  Speech-center,  or  Center  for  the  Reception  of  the  Muscular 

Memories  Necessary  to  Produce  Speech, 47 1 

The  Cortical  Center  for  Writing, 475 

Sensory  Center  for  Writing, 479 


xiv  CONTKXTS. 

Ckrebral  LocALl/ATKiN   {^Continued) —  Page 

The  Centers  which  Preside  over  tlie  Higher  Intellectual  Faculties, 4S0 

The  Cortical  Center  for  the  Special  Sense  of  Taste,      482 

The  Cortical  Center  for  the  Special  Sense  of  Smell 483 

The  Locali/iation  of  Lesions  in  the  Centrum  Ovale, 484 

Lesions  of  the  Centrum  Semiovale  beneath  the  Motor  Area 485 

Centrum  Ovale  of  the  Temporal  Lobe, 486 

Localization  of  Lesions  in  the  Centrum  Ovale  of  the  Parietal  Lobe,  ....  486 

Centrum  Semiovale  of  ihe  Occipital  Lobe,      487 

Lesions  of  the  Corpus  Cailosum, 487 

Localization  of  Lesions  of  the  Internal  Capsule 488 

Basal  Ganglia, 488 

Localization  of  Lesions  of  the  Corpora  Quadrigemina, 488 

Localization  of  Lesions  in  the  Crura  Cerebri, 489 

Localization  of  Lesions  in  the  Pons  Varolii, 490 

Localization  of  Cerebellar  Lesions, 493 

Lesions  of  the  Middle  Lobe,  or  Worm, 493 

Lesions  of  the  Cerebellar  Hemisphere, 494 

Lesions  of  the  Middle  Cerebellar  Peduncle,  . ....  495 

Localization  of  Lesions  in  the  Medulla  Oblongata, 496 

Localization  of  Spinal-cord  Lesions, 499 

The  Divisions  of  the  Cerebral  Cortex  According  to  Flechsig, 506 

CHAPTER  XIIL 

Xwv.  Embryology  of  the  Central  Nervous  System,      508 

The  Development  of  the  Spinal  Cord, 513 

Develojiment  of  the  Medulla  Oblongata, 525 

Cerebellum  and  Pons, 528 

Corpora  (Quadrigemina,  Crura  Cerebri,  and  Aqueduct  of  Sylvius, 530 

The  Third  Cerebral   Vesicle  (Second  Primitive  Vesicle),  Mesencephalon, 

or  Mid-brain, 530 

Optic  Thalami,  Infundibulum,  Pituitary  Body,  Pineal  Gland,  Corpora  Manimillaria, 

and  Optic  Chiasm 531 

Development  of  the  Cerebral  Hentisplieres, 539 

Development  of  the  Commissural  System  of  the  Cerebral  Hemispheres,     .    .  543 

The  Evolution  of  the  Fissures  of  the  Cerebral  Hemisphere, 545 

The  Callosomarginal  Fissure 545 

The  Fissure  of  Rolando, 545 

The  Precentral  Sulcus  or  Fissure, 546 

The  Fissures  or  Sulci  of  the  Island  of  Reil, 546 

The   Various  Fissures  of  the  Frontal,  Parietal,  Temporal,    and   Occipital 

Lobes, 546 

Development  of  the  Cranial  Nerves, 547 

Development  of  the  Olfactory  Lobe, 550 

Development  of  the  Retina  and  Optic  Nerves, 552 

The  Retina 556 

The  Optic  Nerve, 557 

CHAPTER  XIV. 

Technic  of  the  Macroscopic  and  Microscopic  Examination  of  the  Brain  and 

Spinal  Cord, 559 

Virchow's  Method, 560 

Pitres'  Method, 561 

The  Removal  of  the  Spinal  Cord, 563 

Differential  Stains  for  the  Various  Elements  of  the  Nervous  System, 563 

Staining  of  Nerve-cells  after  the  Method  of  NissI, 564 

To  Stain  Nerve-cells  with  Thionin, 564 

Method  of  Bevan  Lewis, 565 

Modification  of  Kronthal's  ISIethod, 565 

Golgi's  Method  for  Staining  Nerve-cells  and  Their  Processes 566 

Golgi's  Rapid  Method, 566 

Golgi's  Slow^  Method, 566 

Berkley's  Method  of  Impregnation, 566 


CONTENTS.  XV 

Technic  of  the  Macroscopic  and  Microscopic  Examination  of  the  Brain  and 
Spinal  Cord  [Continued) —  Page 

Cox's  Modification  of  the  Golgi  Sublimate  Method, 567 

Weigert's  Method  of  Staining  the  Myelin  Sheaths, 568 

Marchi's  Method, ' .    \    .  569 

Neuroglia  Stains, 569 

Differential  Stains  for  Neuroglia  Fibers. — Method  of  Mallory,  .    .    .  569 
Mallory's     Phosphotungstic-acid     Hematoxylin    Method    for 

Staining  Neuroglia, 570 

Stains  for  Axis-cylinder  Processes, 571 

Neutral  Carmin, cn\ 

Nigrosin, 571 

Van  Gieson's  Method, 571 

Stains  for  End  Organs,  Terminations  of  Nerves,  and  Collateral  Branches,    .  572 


Method  of  Gerlach, 
Method  of  Freud, 


572 

572 


Method  of  S.  Ramon  y  Cajal, 572 

Ehrlich's  Vital  Methylene-bkie  Method  (Modified  by  SemiMeyer),    .  573 

General  Stains, cj3 

Hematoxylin, 1:7:5 

INDEX, :::::::::::::::  575 


ILLUSTRATIONS. 


Fig.  Page 

1.  A  Group  of  Multipolar  Nerve-cells  from  an  Anterior  Horn  of  the  Spinal  Cord.     Show- 

ing Nissl  granules  and  pigment  (CfVy/r^i^),  .    .    , 19 

2.  Multipolar  Nerve-cells  from  the  Spinal  Cord  of  an  Ox.    Stained  with  methylene-blue 

and  showing  striation  of  cell-bodies  and  their  processes  (^Colored), 21 

3.  A  Ganglion  Cell  from  an  Anterior  Horn  of  the  Spinal  Cord  of  an  Ox.      Showing  the 

arrangement  of  the  Nissl  granules  and  the  ramification  of  the  dendrites  [Colo-ed),       22 

4.  Section  of  Posterior  Spinal  Ganglion  of  Embryo  Chick.      Illustrating  bipolar  cells. 

{After  Van  Gehtuhfen),        24 

5.  Microphotograph  of  a  Group  of  Multipolar  Nerve-cells  from  the  Anterior  Horn  of 

the  Human  Spinal  Cord.      Stained  with  the  Cox-Golgi  method, 25 

6.  Microphotograph  showing  Purkinje  Cell, 26 

7.  A  Frontal  Section  through  an  (Olfactory  Bulb  of  a  Six- weeks' -old  Cat.      -Showing 

layer  of  granular  cells.     {After  Koelliker^, 27 

8.  Microphotograph  of  Small  Pyramidal  Cells, 28 

9.  Microphotograph  of  Large  Pyramidal  Cells, 29 

10.  A  Group  of  Large  Pyramidal  Cells  from  the  Motor   Area  of  the    Human    Brain. 

Stained  after  the  method  of  Bevan  Lewis, 30 

11.  Nerve-fibers  from  the  Muscle  of  a  Frog  Injected  with  Methylene-blue.     Showing  the 

dark  stained  axis-cylinders,  the  nodes  of  Ranvier,  and  the  separation  of  the  terminal 
axones  into  several  primitive  fibrillje.     {After  Koellike^-^ ,  32 

12.  Medullated  Nerve-fibers  Blackened  by  Osmic  Acid.      {Landois  and  Stirling),  .    .    .       33 

13.  Medullated  Nerve-fibers  (with  Osmic  Acid).      {^Landois  and  Stirling), 33 

14.  A  Bundle  of  Nerve-fibers  Stained  with  Nitrate  of  Silver.      Showing  the  outlines  of 

epithelial  cells  of  the  perineurium.     {After  Ranvie^-),       ,       34 

15.  Remak's  Fiber  from  Vagus  of  Dog.      {^Landois  and  Stirling), 36 

16.  Transverse  Section  of  a  Nerve  (Median).     {Landois  and  Stirling), 37 

17.  Termination  of  Sensory  Nerves  in  Stratified  Squamous  Epithelium.      Golgi  Stain. 

{After  Retzitis), 38 

18.  Vertical  Section  of  the  Skin  of  the  Palm  of  the  Hand.      [Landois  and  Stirling),  .    .       38 

19.  Wagner's  Touch  Corpuscle  from  the  Palm,  Treated  with  Gold  Chlorid.      {Landois 

and  Stirling), 3^ 

20.  Cylindric  End  Bulbs  from  the  Conjunctiva  of  the  Calf.      {Merkel), 39 

21.  End  Bulb  of  the  Human  Conjunctiva,  Treated  with  a  Mixture  of  Acetic  and  Osmic 

Acids.      {IV.  Kratise), 4° 

22.  Articular  Corpuscle  from  Phalangeal  Joint  in  Man.      {W.  Kraiise),    ......       40 

23.  A  Microphotograph  of  Two  Pacinian  Corpuscles  from  the  Mesentery  of  a  Cat,  ...       41 

24.  Tactile  Menisque  from  the  Nose  of  a  Guinea-pig.      {Ranvier), 42 

25.  Organ  of    Golgi  from   the   Human   Tendo   Achillis,    Chlorid  of  Gold  Preparation. 

.■    {After  Ciaccio), 43 

26.  Muscular  Fibers  with  Motorial  End  Plates.      {Landois  and  Stirling), 45 

27.  Motor  Terminations  in  a  Lizard,  Stained  by  Methylene-blue.    {Landois  and  Stirling) 

{Colored), 46 

28.  A   Large  Cell  of  the  Second  Type  of  Golgi  from  the  Granular  Layer  of  the   Cere- 

bellum.     {After  Koelliker)  {Colored), 5^ 

29.  Three  Cajal  Cells  from  the  Cortex  of  the  Gyrus  Fornicatus  of  a  Dog.      {After  Koel- 

liker),         52 

30.  Motor  and  Sensory  Neurones.     { fakob' s  Atlas)  {Colored),  _.       53 

31.  Microphotograph  of  Neuroglia   Cells.      Showing  the  relation  they  bear  to  the  capil- 

lary blood  vessels.      Stained  after  the  Cox-Golgi  method,       55 

32.  Three  Neuroglia  Cells   (Astrocytes).     Showing  the  relation  the  neuroglia  processes 

bear  to  the  cell -body.     {After  Weigert)   {Colored), 57 


xviii  ILLUSTRATIONS. 

Fic;.  I'Ai.K 
^}.    Neuro<;lia  Cells  from  .the  Cerebral  Cortex  of  a  Dog's  Brain.      Showing  their  connec- 
tion with  Mood-vessels.     {After  A'oel/ikrr),  . 59 

34.  A  Capillary  lilood- vessel  fruin  the  Cray  Matter  of  the  .Spinal  Cord  of  an  Ox.      Stained 

with  methylene-blue  and  niagnilied  400  diameters  (Cc/i'/vi/), 61 

35.  A    Camera   Lucida    Drawing  of  a  J'art  of  the  Cray  Matter  of  the  Anterior  Horn. 

Showing  pericellular  and  jierivascular  lymph  channels  (("('/(>;•<•(/),       ...  .    .       62 

36.  View  from  liehind  of  the   Lower   l-^nd   of  the  Sjiinal  Cord  with   the   Cauda  Equina 

and  Dural  .Sheath.      [A//en  Thomson), 66 

37.  Photograph  of  Human  Spinal  Cord 67 

38.  Diagram  .Showing  the  Relative  Size  and  I'orm  of  Different   Segments  of  the  Coccy- 

geal, Sacral,  Lumbar,  Dorsal,  and  Cervical  Cord.      {After  Goivers), 70 

39.  A   Transver.se  Section  of  the  Human  Spinal  Cord  through  the  Mid-lumbar  Region  to 

Show  its  General  Topography.      Weigert's  stain,      ....  71 

40.  Transverse  Section  of  the  Human   Spinal  (^ord  at  the  Level  of  the  Eighth  Dorsal 

Vertebra.      X  ^O-      [LaitJois  and  Stirlhur), 73 

41.  Section  of  the  Isthmus  of  the  Lumbar  Cord.     .Showing  the  central  canal  in  the  mid- 

dle, surrounded  by  the  substantia  gelatinosa  centralis.  [After  E.  A.  Sehafer, 
from  Qi/tn'n), 75 

42.  A  Group   of  Multipolar   Nerve-cells   from  an   Anterior  Horn   of  the  .Spinal  Cord. 

Showing  Nissl  granules  and  pigment  (Co/ored), 77 

43.  Section  of  the  Lumbar  Cord  of  an  Adult.     Showing  the  anteromedian  and  postero- 

lateral groujis  of  cells  (C(i/();-cv/) 79 

44.  Camera  Lucida  Drawing  of  a  part  of  an  Anterior  Horn  with  Adjacent  White  Matter 

of  the  Lateral  Column.  .Showing  nerve-fibers  coming  from  that  column  and 
coursing  between  and  around  the  motor  nerve-cells.  Stained  after  method  of 
Weigert-Pal, 80 

45.  Diagram  of  a  Transverse  Section  of  the  Spinal  Cord.      (After  Starr), 81 

46.  Microphotograph  of  Transverse  Section  of  Cord.      .Showing  nerve-fibers  cut  across,  .       85 

47.  Microphotograph  of  a  Partial  Transverse  Section  of  the  White  Matter  of  the  Spinal 

Cord  of  an  Ox, 87 

48.  Schematic   l\ei)resentation  of  the   Situation   of  the  Various  Tracts  of  Fibers  in  the 

Spinal  Cord 88 

49.  Diagram  Indicating  the  Course  of  the  Motor  and  Sensory  Fibers  of  the  .Spinal  Cord 

and  Medulla  (Co/ored), 93 

50.  Posterior  Cornu  and  Column  at  the  Last  Dorsal  Segment.      {After  Cowers),      ...       97 

51.  Longitudinal   Section   of  the   Cord  in   the  Cervical   Region   of  a  Sheep's  Embryo, 

Twenty-two  Centimeters  long.  .Showing  the  division  of  the  posterior  nerve-fibers 
after  entering  the  cord.      {Landois  and  Stirtiiii^), 98 

52.  Lateral  Column  of  a  New-born   Rabbit, 98 

53.  Transverse   Section  of  the  Spinal  Cord  at  the  Level  of  the  First  Sacral  Segment. 

{After  Alexander  Bruce) lot 

54.  Course  and  Termination  of  Gowers'  Tract       {According  to  Hoche), 103 

55.  Transverse  Section  through  a  Posterior  Spinal  Ganglion.      Stained  after  the  method 

of  Weigert, 109 

56.  A   Group  of  Cells  from   a   Human    Posterior   Spinal    Ganglion.     Stained    after  the 

method  of  Nissl, no 

57.  Schematic   Representation   to  Show   the  Origin   and    Relations  of  the  Anterior  and 

Posterior    Spinal  Nerve-roots,  Ill 

58.  A  Section  through  the   Spinal  Cord  of  a  New-born  Mouse.      Showing  reflex  collat- 

erals from  posterior  nerve-roots  terminating  about  the  nerve-cells  of  the  anterior 
horn.     {After  Letthossek), 1 13 

59.  Diagram  Showing  the  Relative  .Size  and   Form  of  Dififerent  Segments  of  the  Coc- 

cygeal, Sacral,  Lumbar,  Dorsal,  and  Cervical  Cord.      {After  Gowers), 1 15 

60.  Transverse  Section  through  a  Sacral  Segment  of  the  Spinal  Cord.    Weigert  preparation,     1 16 

61.  A  Section  through  the  Spinal  Cord  of  a  Human  Fetus,  Twenty-three  Centimeters  in 

Length.  Showing  the  central  canal  with  its  substantia  gelatinosa  centralis  and 
ependymal  cells.      [After  Lenhossek), II8 

62.  Transverse  Section  of  the  Spinal  Cord  of  a  Human  Embryo,  Fourteen  Centimeters  in 

Length.      Illustrating  the  distribution  of  neuroglia.      {After  Lenhossek), 1 19 

63.  A  Transverse  Section  through  a  Segment  of  the  Dorsal   Cord,  to  .Show  the  General 

Arrangement  of  Neuroglia.      Nigrosin  stain  (6W(p;W), 120 

64.  A  Camera  Lucida  Drawing  of  a  Field  of  the  Lateral  Column  of  Figure  63.    Nigrosin 

stain  {Colored), 121 

65.  Scheme  to  Show  the  Course  and  Distribution  of  the  Terminal  Branches  of  the  .\rte- 

rial  Plexus  of  the  Pia  Mater.     {After  Van  Celiuchten\ 123 


ILLUSTRATIONS.  xix 

Fig.  Page 

66.  View  from  Before  of  the  Medulla  Oblongata,  Pons  Varolii,  Crura  Cerebri,  and  Other 

Central   Portions  of  the   Encephalon  (^Natural   size).      {Allen    Thomson.) — [From 
Quahi's  '■'■  Anatomy  ^^), 1 27 

67.  View  of  the  Medulla  Oblongata,  Pons  Varolii,  Crura  Cerebri,  and  Central   Parts  of 

the  Encephalon  from  the  Right  Side.     [Quain'' s  '■'•  Anatomy .'''') — [Allen  Thomson'),     129 

68.  Posterior  and  Lateral  View  of  the  Medulla  Oblongata,  Fourth  Ventricle,  and  ^lesen- 

cephalon  (Natural  size).     [E.  A.  S.) — [Fro7)i  Qiiatn''s  '^  Anatotny '') , 133 

69.  Transverse  Section  through  the  Medulla  Oblongata  at  the  Beginning  of  the  !Motor 

Decussation.     [After  Koelliker), 137 

70.  Diagram  of  the  Structure  of  the  Medulla  Oblongata.      [From  Gowers''  '■'Diseases  of 

the  N^ervous  System''^), 13S 

71.  Transverse    Section    of   the   Medulla    Oblongata  through   the    Motor   Decussation. 

[After  Henle), 141 

72.  Transverse  Section  of  the  Medulla  at  the  Beginning   of  Hypoglossal  Nerves.      The 

pyramidal  or  motor  decussation  is  complete.      [After  Henle), 142 

73.  Section  of  the  Medulla  Oblongata  at  About  the  iliddle  of  the  Olivary  Body.    [After 

Sckwalbe.) — [Fro7)i  Quain^s  ''Anatomy  "), ...     143 

74.  Section  of  Medulla  Oblongata  at  Level  of  Sensory  Crossway.    Weigert-Pal  preparation,   145 

75.  Diagram  Indicating  the  Course  of  the  Motor  and  Sensory  Fibers  of  the  Spinal  Cord 

and  Medulla  [Colored), 147 

76.  Section  Through  Formatio  Reticularis  of  the  ]\Iedulla  Oblongata.      Method  of  Wei- 

gert-Pal,       150 

77.  Microphotograph  from  a  Seven-months'  Human  Fetus  of  Section  of  Formatio  Retic- 

ularis Grisea.     The  cells  with  their  decussating  axones  are  seen, 151 

78.  Transverse    Section    through    the   Hypoglossal   Nucleus.       Method  of  Weigert-Pal 

[Colored), ^ 153 

79.  Medulla  Oblongata  from  a  Human  Embryo  of  Eight  Months.      [After  Koelliker),     .     156 

80.  Transverse  Section  through  the  Medulla  of  a  Mouse  at  the  Level  of  the  Commissural 

Nucleus.      [After  Ramon  y  Cajal), 157 

81.  Microphotograph  Showing  Multipolar  Cells  of  Inferior  Olivary  Body, 159 

82.  Hemisection  of  Medulla  to  Show  Olivary  Body.     Method  of  Weigert-Pal,   ....  161 

83.  The  Cerebello-olivary  Tract.      [After  Edinger), 165 

84.  Transverse  Section   through  the   Pons  Varolii.      Illustrating  the  origin  of  the  sixth 

and  seventh  cranial  nerves, 167 

85.  Lateral  View  of  the  Medulla  Oblongata  with  the  Schematic  Representation  of  the  Nu- 

clei and  the  Intramedullary  Course  of  the  Cranial  Nerves.      [From  Jakob's  Atlas) 
[Colored), 169 

86.  Transverse   Section   through   the   Distal  Part  of  the  Pons  of  an  Eight-months'  Hu- 

man Embryo.      (After  Koelliker),  .  172 

87.  Microphotograph  Showing  Cells  of  Ventral  Auditory  Nucleus.      Method  of  Golgi,     .     173 

88.  Dorsal  Part  of  a  Transverse  Section  of  the  Medulla  Oblongata  from  a  Human  Em- 

bryo of  Six  Months.      [After  Koelliker), 174 

89.  Transverse  Section  through  Upper  Part  of  Pons  Varolii.      Method  of  Weigert-Pal,  .     178 

90.  Transverse  Section  through  the  Pons,  in  the  Region   of  the  Crossing  of  the  Fourth 

Nerve  in  the  Dorsal  Medullary  Velum.      [After  Koelliker) 181 

91.  Lateral  Sagittal  Section  through  the  Pons  and  Cerebellum  of  a  Fetal  Mouse.      [After 

Ra}nd7i  y  Cajal),_ 183 

92.  Section  through  Medulla  of  a  Human  Fetus  of  Seven  Months.      Showing  axones  and 

collaterafs  of  the  trigeminal  nerve  entering  the  enlarged  caput  posterioris,    ....     184 

93.  Figure  Showing  the  Three   Pairs  of  Cerebellar  Peduncles.       [After  Hirschfeld  and 

Level  lie,  from  Sappey),     .  187 

94.  Superior  Surface  of  the  Cerebellum, 191 

95.  Inferior  Surface  of  the  Cerebellum, 19^ 

96.  Microphotograph  of  Cerebellar   Cortex.     Showing  the  molecular  and  granular  lay- 

ers and  the  arrangement  of  the  arbor  vitse,     193 

97.  Section   through   Cerebellum  to  Show  the  Dentate  Nuclei  and  White  Matter  of  the 

Hemispheres, ^95 

98.  Microphotograph  of  a  Section  through  the  Corpus  Dentatum  of  the  Human  Cerebel- 

lum.    Containing  three  large  (multipolar)  polygonal  cells.      Method  of  Berkley,  .     195 

99.  Microphotograph  Showing  Basket  Cells   and  Fibers  Surrounding  the  Bodies  of  Two 

Purkinje  Cells  (Human  Cerebellum).      Cox-Golgi  method, 197 

100.  Granular  Cells  of  the  Inner  Layer,  with  Ascending  Neuraxones  branching  J-shaped 

to  Form  the  Horizontal  Fibers  of  the  Molecular  Layer.     [After  Van  Gekuchten),  .     198 

101.  Microphotograph  Showing  the   Moss-like   Fibers  of  the   Cerebellum.       Cox-Golgi 

Method,      .,..-. 199 


XX  ILLUSTRATIOxVS. 

Fig.  •  Page 

102.  Microphotograph  of  Purkinje  Cell 201 

103.  Scheme  of  the  Fibers  Passing  to  and  from  the  Cerebellum, 205 

104.  Schematic  Representation  of  the  Different  Constituents  of  the  Cortical  Gray  Matter  of 

the  Cerebellum.      [After  I'titi  Gehucliti-n), 208 

105.  Lateral  view  of  Mesencephalon,  J'ons,  and  Medulla.    {Gr^eitbatier), 21 1 

106.  Metencephalon,  Mesencephalon,  and  Thalamencephalon,  from  the  Dorsal  Surface. 

[After  Obersteiner), 212 

107.  Microphotograph  of  a  Transverse   Section   through   the  Corpora  Quadrigemina  of  a 

Sheep.     Showing  layer  of  superficial  cells.      Method  of  Berkley, 213 

108.  A  Characteristic  Cell  from  the  Third  (Gray)  Layer  of  the  Optic   Lobe  of  an  Eigh- 

teen day-old  Chicken.      Golgi's  method.      {After  Koellikcr), 215 

109.  Schematic  Representation  of  the  Essential    Histologic  Elements  of  the  Optic  Lobe 

of  a  Bird.     Showing  the  probable  route   taken    by  visual  impressions  to   reach   the 

cerebral  (occipital)  cortex.      [After  Koeliiker)  [Colored^, 217 

no.    Transverse   Section   through   the    Corpora    Quadrigemina    from   an    Eight-months' 

Human  Fetus.     [After  Koelliker") .219 

111.  Transverse  .Section  through  the  Mid-brain  of  an  Adult.       Weigert's  method,  .    .    .    .     221 

112.  Diagram  of  Section  of  the  Crus.      [Modified from  Wernicke,  frovi  Gtnvers),  ....     222 

113.  Diagram  Indicating  the  Course  of  the  Motor  and  .Sensory  Fibers  of  the   Spinal  Cord 

and  Medulla  [Colored), 225 

114.  Transverse  -Section  through  the  Spinal  End  of  the  Posterior  Corpora  Quadrigemina  of 

a  Cat.      Weigert  preparation.      [Ajter  Koelliker), 227 

115.  Horizontal  Section  through  the  Cerebellum, 229 

116.  Microphotograph  through  the  Red  jXuclei  of  the  Mid-brain  of  a  Young  Sheep.    Show- 

ing decussation  of  the  libers  of  the  superior  cerebellar  peduncles.     Method  of 
Golgi, 231 

117.  Microphotograph  of  a  .Section  through  the   Red  or  Tegmental  Nucleus  of  a  Young 

Sheep.     Showing  seven  of  its  characteristic  cells.      Golgi  method, 231 

118.  Course  and  Termination  of  Go wers'  Tract.      [Accorditig  to  Hoc/ie), 234 

119.  Microphotograph   through  the  Nucleus  of  Origin  of  the  Motor  Oculi  Nerve.      Show- 

ing the  multipolar  cells  of  this  nucleus.      Golgi  preparation,        236 

120.  A  Camera  Lucida    Drawing   through   the   Nuclei   of  Origin   of  the   Third  or  Motor 

Oculi  Nerves.     Showing  the  location  of  the  nuclei  and  their  cells,  together  with  the 
descending  axones  from  those  cells  which  go  to  form  the  nerve-roots  [Colored),      .     237 

121.  Diagram  of  the  Groups  of  Cells  Forming  the  Nuclei  of  the  Third  and  Fourth  Cranial 

Nerves.      [After  Perlia.frovi  Quain), 238 

122.  Transverse  Section   through   the   Mid-brain  at   the   Level  of  the   Posterior  Corpora 

Quadrigemina.     Weigert  preparation, 239 

123.  Schematic  Representation  of  the  Origin  of  the  Trigeminal  Nerve.      [After  Edinger),    241 

124.  Horizontal   Section   through  the  Cerebral  Hemispheres  to   Show  the   Region  of  the 

Third  Ventricle, 245 

125.  Section  through  the  Superior  Part  of  One  of  the  Superior  Corpora  Quadrigemina  and 

the  Adjacent    Part  of   the    Optic  Thalamus.      [After  Meynert.) — [From  Qiiaiii s 
'^AnatoMv"),         250 

126.  Frontal  Section  through  Basal  Ganglia  to  Show  the  Nuclei  of  the  Optic  Thalamus. 

[After  von  Monakoiu.) — [From  Starr  s  "■Atlas"), 15 1 

127.  Microphotograph  through  Optic  Thalamus  Showing  Busch  Cells.      Golgi  method,     .  252 

128.  Microphotograph  through  Optic  Thalamus  Showing  Stellate  Cells.   Method  of  Golgi,  255 

129.  Microphotograph    through  Optic  Thalamus  with  a  Single    Large   Polygonal   Cell. 

Method  of  Berkley 255 

130.  A  Perpendicular  Section  through  the  Brain  of  a  Rabbit  Lateral  to  the  Corpus  Mam- 

millare.     [After  Koelliker), 257 

131.  Section    of    Corpora   Quadrigemina.     Showing   cells   of  red  nucleus.     Cox-Golgi 

method, 261 

132.  Diagrammatic  Section  of  the  Human  Retina.    [Schtiltze.) — [After  Quain) 264 

133.  Section  through  the  Retina  of  a  Mammal  to  Show  Layer  of  Horizontal  Cells  of  the 

External  Molecular  Layer  and  the  Spongioblasts  of  the  Internal  Molecular  Layer. 
(After  Ramon  y  Cajal), 265 

134.  The  Essential  Elements  in  the  Retina  of  a  Dog.      [After  Van  Gehuchten),    ....     267 

135.  The  Origin  and  Relation  of  the  Optic  Tract.      [G.  D.   Thane.) — [From  Quain),     .     268 

136.  Microphotograph  through   Optic  Thalamus  of  a  Sheep.      Showing  fibers  from  optic 

nerve  terminating  about  stellate  cells.      Method  of  Berkley, 269 

137.  Diagram  of  the  Corpora  Quadrigemina  Anterior, 271 

138.  Horizontal  Section  through  the  Optic  Chiasm  of  a  Child.      [After  A'oelliker],  .    .    .  274 

139.  Frontal  Section  through  the    Interbrain.     [After Koelliker), 275 


ILLUSTRATIONS.  xxi 

Fig.  Page 

140;  -Sagittal   Section  of  the    Pituitary    Body  and   Infundibulum  with    Adjoining  Part  of 

Third    Ventricle.     {Sc/nualbe,  from    Qtiain), 277 

141.  Examples  of  Some  of  the  Various  Forms  of  Pyramidal   Cells  Found  in  the  Ventral 

Part  of  the  Posterior  Lobe  of  the    Pituitary  Body.      [A/ler  Berkley), 278 

142.  Medisection   of  Brain,  Showing   Important  Sinuses 282 

143.  Section  of  the   Posterior  and  Lower  Parts  of  the   Brain  within  the   Skull  to  Exhibit 

the  Subarachnoid  Space  and  Its  Relation  to  the  Ventricles.      [After  Key  and  Ret- 
zius.) — [From  Quain), 286 

144.  Coronal   Section   through  the   Great  Longitudinal  Fissure,  Showing  the  Meninges. 

[Key  and  Retzius), .         .     287 

145.  Vertical  Section  of  the  Cortex  Cerebri  and  its  Membranes.     X  ^j^.     [After  Landois 

and  Stirlingl , 289 

146.  View  of  the   Upper  Surface  of  the  Velum  Interpositum,  Choroid  Plexuses,  and  Cor- 

pora Striata.      [From  Sappey,  after  Vicq  d'  Azyr), 290 

147.  Photograph  of  the  Superior  Surface  of  the  Cerebrum,      295 

148.  Photograph  of  the  External  Surface  of  the  Brain 297 

149.  Photograph  of  the  Median  Surface  of  the  Brain,      301 

150.  Vertical  Section  through  Frontal  Lobe, 301 

151.  Diagrammatic  Representation  of  the  Lobes  of  the  Cerebrum, 305 

152.  Frontal  Section  through  Parietal,  Temporal,  and  Occipital  Lobes,  Together  with  the 

Cerebellum, 307 

153.  Photograph  of  the  Superior  Surface  of  the  Cerebrum, 311 

154.  Longitudinal  Section  through  Cerebral  Hemisphere  to  show  the  Centrum  Semiovale 

of  the  Frontal,  Parietal,  Occipital,  and  Temporal  Lobes, 313 

155.  Convolutions  of  the  Mesial  Surface  of  the  Cerebrum, 315 

156.  Section  through  Left  Gyrus  Hippocampus.      Showing  the  formation   of  the  hippo- 

campus major.     Method  of  Weigert-Pal, 317 

157.  Photograph  of  the  Base  of  the  Human  Brain, 321 

158.  Olfactory  Lobe  of  the  Human  Brain.      [I/is.) — [After  Qieatn), 327 

159.  A  Schematic  Representation  of  the  Principal  Elements   of  the   Olfactory  Bulb  of  a 

Mammal.      ( Fan  Gehuchten), 3^9 

160.  Mitral  Cells  from  a  Mouse  Twenty-four  Days  Old.     [After  Koelliker), 331 

161.  A  Frontal  Section  through   an   Olfactory  Bulb  of  a   Six-weeks'-old  Cat.      Showing 

layer  of  granular  cells.     [After  Koelliker), 333 

162.  Sections  of  Cerebral  Convolutions.     [After  Baillarger,  from  Qtiain), 339 

163.  A  Scheme  of  the  Distribution  of  the  Nerve-fibers  of  the  Cerebral  Cortex.     According 

to  the  views  of  Meynert,  Obersteiner,  Edinger,  and  Dejerine.      [After  Dejerine),  .     340 

164.  A  Scheme  Showing  the  Development  of  our  Knowledge  of  the  Different  Cell-layers 

of  the  Human  Cerebral  Cortex  from  the  Time  of  Vicq  d'Azyr,  in  1790,  to  the  time 

of  Cajal,in  1890.      [After  Dejerine)  [Colored), 341 

165.  A  Cajal  Cell  in  Course  of  Development  from  Section  of  Ascending  Frontal  Gyrus  of 

a  Human  Fetus  at  Eight  Months.     [After  Retzius), 344 

166.  Microphotograph  of  Small  Pyramidal  Cells, 345 

167.  Microphotograph  of  Large  Pyramidal  Cells, 347 

168.  Cells  with  Ascending  Axones  from  the  Cortex  of  the   Gyrus   Fornicatus  of  a   Six- 

days' -old  Mouse.-     [After  Koellike}'), 34^ 

169.  Microphotograph  of  Polygonal  Cell  of  the  Fourth  Layer  of  the  Cerebral  Cortex  of  a 

Mouse's  Brain, 349 

170.  Diagram  of  the  Cells  of  the  Cerebral  Cortex.      [After  Starr), .    351 

171.  Section  through   Left  Gyrus    Hippocampus.      Showing  the  formation  of  the  hippo- 

campus major.     Method  of  Weigert-Pal, ' 353 

172.  Microphotograph  of  a   Frontal  Section  through  the  Brain  of  a  Mouse.    Showing  the 

peculiar  involution  of  the  gyrus  hippocampus  as  it  forms  the  cornu  ammonis,  .    .    .     354 

173.  Microphotograph  of  Cornu  Ammonis  of  a  Dog's  Brain.     Showing  contour  and  for- 

mation of  cornu   ammonis, 355 

174.  Microphotograph    of    Cornu    Ammonis    of   a    Rat's     Brain.      Showing   three  large 

pyramidal  cells,      357 

175.  Microphotograph  through  Cornu  Ammonis.      Showing  the   deep  part  of  the   superfi- 

cial layer,  or  stratum  lacunosum, 35^^ 

176.  Microphotograph  of  Section   through   Cornu   Ammonis  and   Gyrus  Dentatus  (Rat's 

Brain).      Showing  a  group  of  small  pyramidal  cells  of  the  gyrus  dentatus,  ....     360 

177.  Microphotograph  of  Small  Pyramidal  Cells  of  the  Gyrus  Dentatus  and  their  Axones, 

P^orming  the  Moss-like  Fibers, 361 

178.  Horizontal  Section  of  the  Cerebrum  above  the   Corpus   Callosum  to  Show  the   Cen- 

trum Ovale.      [After  Van  Gehuchten), 3^3 


xxii  ILLUSTRATIOXS. 

Fig.  P.M.I-: 

179.  Cortex  of  Human  Itiain.    Showing  tlie  nerve-fiber  systems  and  plexuses.     Weigert's 

and  fiolgi's  method  combined.  {After  Andriezcn,  from  Starr  s  ^'^  Atlas"),  .  .  .  365 
I  So.    Diagram  of  the   Association-tibers  of  the   Cerebral    Hemisphere,      (/s.  A.  S.,  after 

Mty»ert,from  Qtiain), 367 

iSi.   Semidiagrammatic  Re]>resentation  to  Show  the  Kasciculus  Occipitofrontaiis,  the  Txnia 

Semiciiculiiris,  and  the  l-'asciculus  Uncinatus.      {After  De/eriiie),       369 

182.    A  Scheme  to  Show  tiie  Origin  and  Termination  of  tiie   l-ibers  of  tlie   Corpus  Callo- 

sun).      [After  Van  Gehm/iten),       370 

1S3.    Micropholograph  Showing  the  Radiation  of  tiie  Fibers  Composing  the  Corona  Radi- 

ata  of  a  Rat's   lirain.      Method  of  tioigi 372 

184.    Diagrammatic  Arrangement  of  tlie  Projection  Tracts  Connecting  the  Cereliral  Cortex 

witli  the  Lower  Xerve-centers.      (After  Starr), 374 

1S5.   Diagram  to  Sliow  the  Relative  Position  of  the  Several  Motor  Tracts  in  Their  Cour.se 

from  the  Cortex  to  the  Crus.      {.Ifter  Gtnoers), 375 

186.  Diagram  of  the  Course  of  the  Motor  Tract  as  Shown  in  a  Diagrammatic  Horizontal 

Section  through  the  Cerebral  Hemisphere,  Pons,  and  Medulla.      (.Ifter  Gorcers),  .     377 

1 87.  Diagram  Indicating  the  Course  of  the  Motor  and  Sensory  Fibers  of  the  Spinal  Cord 

and  Medulla  (Co/ored), 379 

188.  Diagram  of  the  Course  of  the  Pyramidal  or  Motor  Tract  of  the  Right  Hemisphere. 

(After  Goioers) ' 381 

1S9.    (After  Sac/is).     I.  Sensory  Tract.     IT.    Horizontal  Section  of  Cord.      HI.    Relation 

of  Motor  Tract  to  Nuclei  of  Cranial  Nerves.      (After  /-/atatt)  (Co/ored  ),     ....     383 

190.  Horizontal  Section  of  Cerc-brum  above  the  Corpus  Callosum  to  Show  the  Centrum 

Ovale.      (After  Van  Geliuchten) 388 

191.  Portion  of  a  Median  Section  of  the  lirain, 3^9 

192.  \'iewof  the  Cori>us  Callosum  from  .\i)ove.     { Front  Sappcy,  after  Fcnnlle, from  Qtiain),  390 

193.  Photograph  of  Horizontal  Section  through  Cerebrum  to  Show  Lateral  Ventricles,      .  39I 

194.  View  from  Above  and  the  Side  of  the  Whole  Left  Lateral  \"entric!e.      Natural  size. 

(E.  A.  S.  and  G.  D.  T.,  from  Qiiain), 395 

195.  Two  \'iews  of  a   Plaster  Cast  of  the  Cavities  of  the  Cerebral  \'entricles.      (After 

IVehker,  from  Qttai'n), 397 

196.  Photograph  of  a  Section  through  the  Frontal  and  Tip  of  Temporal  Lobes,     ....  398 

197.  Photograph  of  .Sagittal  (Longitudinal)  Section  through  a  Cerebral   Hemisphere,     .    .  400 

198.  IMicrophotograph  of  Large  Rectangular  Ceils    of   Corpora   Striata.      Colgi    method. 

(After  Starr), 40I 

199.  Diagram  of  a  Section  through  the  Crus,  etc.,  in  Front  of  the  Corpora  Quadrigemina. 

(Modified front  Wei-nicke) 402 

200.  Scheme  Showing  the  Tractus  -Striothalamicus.      (After  Edinger), 404 

201.  Photograph  of  a   Longitudinal   Section    through    a    Cerebral   Hemisphere  to  Show 

the  Canglia  of  the  Hemisphere, 405 

202.  Photogra]ih   of  a    Horizontal    Section   Through    a  Cerebral   Hemisphere   to    Show 

Relations  of  Internal  Capsule,     .' 4^9 

203.  Horizontal  Section  through  the  Right  Hemisphere  of  a  Man.    (After  von  Afonako7o) 

(Colored) 41 1 

204.  Distrii)ution  of  Arteries  in  the  Cerebral  Cortex.      (After  D,!i ret), 417 

205.  The  .Arteries  of  the  Base  of  the  Cerebrum.     (G .  D.  T. , after  Dnret, and  from  Nature, 

from  Qiiain)  (Colored), 419 

206.  Cortical   Distribution  of  the   Middle  Cerebral  Artery  (Diagrammatic).     (G.D.   T., 

after  Charcot,  from  Qiiain)  (Colored), 422 

207.  Diagram  of  the  I)lood-supply  to  the  Central  Ganglia  by  the  Lenticulostriate  Arteries, 

External  (E\  and  Internal  (/).      (After  Dnret), 423 

208.  Diagram  Showing  the  .\reas  of  Cortical  Distribution   of  the   Anterior,  Middle,  and 

Posterior  Cerebral  Arteries  Respectively.     (E.  A.  S. ,  from  Qniin), 426,  427 

209.  Arteries  of  the  Anterior  Surface  of  the  Pons  and  Medulla.      (After  Dnret),  ....    429 

210.  Arteries  of  the  Posterior  Surface  of  the  Medulla.      (After  Dnret), 430 

211.  Anterior  and  Posterior  Median  Arteries  of  the  Pons  and  Medulla.      (After  Dnret),  .     433 

212.  Diagram   to  Show    Plan   of  Distribution   of  the   Arteries   of    the   Medulla.      (After 

Dtiret) 434 

213.  Superficial  Veins  of  the  Base  of  the  Brain.      (After  Testnt), 436 

214.  Superficial  Veins  of  the  Internal  Surface  of  the  Left  Hemisphere.     (After  Testnt),  .  437 

215.  Superficial  Veins  of  the  External  Surface  of  the  Left  Hemisphere.       (After  Testnt),  438 

216.  Veins  of  Galen,  or  the  Deep  Cerebral  Veins.      (After  I'an  Ge/inel/ten],     ....  439 

217.  Diagram  Showing  Communications  Existing  between  the  Lateral  and  Cavernous  Sin- 

uses and  the   External  Veins,  indicated  in    Figure  by*.      (After  Lenbe) — (From 
Loomis  and  Thompson, '■'■  Practice  of  Medicine'"''), 44 1 


ILLUSTRATIONS.  xxiii 

Fig.  Page 

219.  Plan  Showing  the  Relative  Position  of  the  Structures  in  the    Right  Cavernous  Sinus, 

Viewed  from  Behind.      [After  Gray), 446 

218.    Medisection  of  Brain,  Showing  Important  Sinuses, 444 

220.  Diagram  of  the  Motor  Areas  on  the  Outer  Surface  of  a  Monkey's  Brain.      [Horsley 

and  Schdfer,  from  Laiidois  and  Stirling), 449 

221.  Diagram  of  the  Motor  Areas   on  the   Marginal   Convolution   of  a  Monkey's  Brain. 

[Horsley  and  Schdfer,  from  Landois  and  Stirling), 450 

222.  A  Drawing  of  the  Left  Cerebral  Hemisphere  (Human)  [Colored'), 451 

223.  A  Drawing  of  the  Right  Cerebral  Hemisphere  (Human)  [Colored), 452 

224.  Position  of  the  Arm-center.      [After  Cowers), 453 

225.  Position  of  the  Center  for  the  Face  and  Tongue.      [After  Cowers), 453 

226.  Cortical  Visual  Centers  on  the  Outer  Surface  of  the  Hemisphere.    [After  Cowers),  .  458 

227.  Inner  Aspect  of  the   Right  Hemisphere.      [After  GoTvers), 45S 

228.  Diagram  of  Course  of  Optic   Nerve-fibers  from   the  Cortex  to   the   Retina.      [After 

Sahli,  Modifed  and  Extetided,  from  Tyson), 459 

229.  Situation  of  Lesions  Causing  Word-deafness  Only.      [From  Starr), 467 

230.  Situation  of  Lesions  Causing  Word-blindness  Only.      [From  Starr), 469 

231.  Situations  of  Lesions  Causing  Aphasia.     [After  Sta7'r,frot?i  Tyson), 472 

232.  Diagram  Showing  Location  of  Tumor  which  Produced  Complete  Agraphia  (Author's 

Case) _ _ 475 

233.  View  from  Before  of  the  Medulla  Oblongata,  Pons  Varolii,  Crura  Cerebri,  and  Other 

Central  Portions  of  the   Encephalon  (Natural  size).       [Allen    Thomson) — [From 

Qiiain's  '^Anato)ny"), 491 

234A.  Diagram  of   Skin  Areas  Corresponding  to  Definite  Spinal  Segments.  [From  Tyson, 

after  Starr),  . 497 

234B.  Diagram  of  Skin  Areas  Corresponding  to  Different  Spinal  Segments.  [From  Tyson, 

after  Starr), 498 

235.  Diagram  (Framed  from  an  Original  Investigation)  Showing  the  Relation  of  the  Ver- 

tebral Spines  to  Their  Bodies  and  to  the  Origin  of  the  Several  Nerve-roots.  [After 
Cowers), 500 

236.  Diagram  of  Lesions  Showing  Brown-Sequard's  Paralysis.   [After  Starr,  from  Tyson),    503 

237.  Schema   Showing   Chief  Symptoms  in    Left   Unilateral   Lesion  of  the  Dorsal  Cord. 

[After  Erb,from  Tyson),         5^3 

238.  Sections  Showing  Stages  in  the  Conversion  of  the  Medullary  Groove  into  the  Neural 

Canal.      [E.  A.  S.,from  Quain) 509 

239.  Longitudinal  Section  of  Head  of  a  Four-and-a-half-day  Chick.      [After  Von  Mihal- 

kovics,from  Edinger),       5'^ 

240.  Fore-part  of  the   Embryo   Viewed   from   the   Dorsal   Side.      [After  Koelliker,  from 

Quain), 514 

241.  Myelospongium  from  Spinal  Cord  of  Three-and-half-weeks'  Human  Embryo.    [His, 

from  Qiiain) S'^S 

242.  Inner  Ends   of   Spongioblasts   with   Germinal    Cells   between    Them.      [His,  from 

Quain), 5^5 

243.  Inner  Ends  of  Spongioblasts.      [His,  from  Quain), 5^5 

244.  Three  Neuroblasts,  Each  with  a  Nerve-fiber  Process  Growing  out  Beyond  the  Base- 

ment Membrane  of  the  Embryonic  Spinal  Cord.      [His,  from  Qiiaiji), 515 

245.  Ependymal  Fiber  of  Marrow   of  a  Seven-days'-old  Embryo  of  a   Chicken.       [After 

Colgi) 517 

246.  Lower  End  of  the  Spinal   Cord  of  a  Human   Embryo  of  Three   Months.      [From 

Minot), 518 

247.  Section  of  Spinal  Cord  of  Four  Weeks'  Human  Embryo.      [His, from  Quain),    .    .    .     519 

248.  Transverse  Section  of  the  Cervical  Part  of  the  Spinal  Cord  of  a  Human  Embryo  of 

Six  Weeks.      [Afer  Koelliker,  from  Qitain) _.    ...     5^9 

249.  Transverse    Section    of    the   Spinal    Cord  from    the    Upper  Dorsal    Region    of  a 

Human  Embryo  of  Six  Weeks.      [After  His,  from  Minot),     ..........     521 

250.  Sections  across  the    Region   of  the  Calamus   Scriptorius   of  the   Brain.      [His,  from 

Quain), 5^3 

251.  Sections  across  the  Fourth  Ventricle   of  a  Somewhat  Older  Embryo.      [His,  from 

Quain), 5^3 

252.  Sections  across  the  Lower  Half  of  the   Fourth  Ventricle  of  a  still   Older   Embryo. 

[His,  fr  0771  Quai7i), 5^3 

253.  Transverse  Section  of  the  Medulla  Oblongata  of  His'  Embryo  Ru.     [After  W.  His, 

f7-07H  Minot) -    •         526 

254.  Transverse  Section  of  the  Medulla  Oblongata  of  His'  Embryo  Mr.      [After  IV.  His, 

from  Aliftot), 5^7 


xxiv  ILLUSTRATIONS. 

Fig.  Page 

255.  Median  Section  through  the  Brain  of  a  Two-and-a-half-niontlis'  Fetus.     (//«,  ft  out 

Qitaitt^, 529 

256.  Fetal  Brain  of  the  Third  Month.      {His,  from  Quain), 5JI 

257.  Transverse  Sections  through  the  Brain  of  a  Sheep's  Embryo  of  2.7  Centimeters  in 

Length.     (AfUr  Koellikei,  from  Oiiain), 533 

258.  Brain  of  a  Chick  Embryo,  Fourth  Day.      {After  Duval,  from  Mi}iot\, 535 

259.  Three  Section.s  through  the  Fore-brain  of  a  Four-and-a-half-weeks'  Embryo.      {His, 

from  Quain) 537 

260.  The  Surface  of  the  Fetal  Brain  at  Six  Months.      (Ji.   Wagner,  from  Quain),      .    .    .     540 

261.  Brain  of  a  Human   Embryo  of  about  Three  Months  (According  to  Marchand,  four 

months).      {After/''.  Marchand,  from  Minot), 541 

262.  Fetal  Brain  of  the  Beginning  of  the  Eighth  Month.      {Mi halkovics,  from  Quain),      ,  544 

263.  Sections  across  the  Hind-brain  of  a  Human  Embryo,  lo  mm.  Long,  {//is, from  Quain),  548 

264.  Section    from   the   Same    Embryo   at   the    Exit   of  the    Facial  Nerve.      {//is,  from 
Quain), 549 

265.  Cranial  Nerves  of  a  Human  Embryo,  10.2  mm.  Long,     {//is,  from  Quain),  ....     550 
266 A.  1  train  of  Chick  of  Second  Day,  viewed  from  below,  to  show  the  formation  of  the 

optic  vesicles  by  outgrowth  of  the  side  of  the  fore-brain,  and  at  the  same  time  by 
the  folding  over  of  the  enlarged  part,  the  proiluction  of  a  grooving  or  cup|)ing  of  the 
vesicles,  {//is,  from  Quain.)  B.  Brain  of  Human  Embryo  of  Three  Weeks. 
Showing  the  primary  optic  vesicles  as  outgrowths  from  the  fore-brain,  {//is.  from 
Quain), 553 

267.  Side  View  of  Anterior  Part  of  Brain  of  More  Advanced  Human   Embryo.      Showing 

the  ])rimary  optic  vesicle  folded  and  tucked,      {//is,  from    Quain) 553 

268.  Side  View  of  the  Same  Part  of  the  Brain  in  a  still  more  Advanced  Embryo,  the  Eye 
Having  Been  Cut  Away,      {//is,  from  Quain), 553 

269.  Rabbit    Embryo  of  Ten  and  One-half  Davs;    Section  of  the  Lens  Anlage.  {Fiom 
^'^^'"of) .....' 555 

270.  Vertical  Section  of  the  Eye  of  a  Chick  Embryo  of  the  Third  Day.     {From  J\/inot),  .  555 

271.  Rabbit  Embryo  of  Thirteen  Days;   Section  of  the  Eye.      {From  J\/inot), 556 


INTRODUCTION 


That  the  comprehension  of  the  normal  and  abnormal  activities 
of  an  organ  must  be  based  upon  an  understanding  of  its  structure 
is  a  truth  as  old  as  Galen,  and  certainly  there  can  be  no  doubt 
that  a  knowledge  of  the  anatomy  of  the  nervous  system  is 
absolutely  essential  to  a  clear  understanding  of  its  diseases. 
While  teachers  of  the  diseases  of  other  organs  have  usually 
been  content  to  refer  their  students  to  the  greneral  anatomic 
course  for  details  of  the  anatomy  of  those  organs,  teachers 
of  the  diseases  of  the  nervous  system  have  almost  universally 
included,  both  in  their  text-books  and  in  their  lectures,  a  more  or 
less  complete  account  of  the  anatomy  of  the  brain  and  spinal 
cord  ;  not  alone  because  the  symptoms  of  nervous  diseases 
can  only  be  explained  by  constant  reference  to  the  anatomy  of 
the  nervous  organs,  but  also  because  in  the  eeneral  anatomic 
course  the  finer  details  of  the  peculiarly  complex  anatomy  of 
the  nervous  system  are  neither  sufficiently  described  nor  demon- 
strated. 

With  one  or  two  exceptions  the  text-books  on  nervous  dis- 
eases continue  to  present,  along  with  the  pathology,  more  or 
less  of  the  anatomy  of  the  nervous  system  ;  but  many  of  the 
teachers  of  this  subject  have  of  late  years  confined  themselves 
rather  strictly  to  its  pathology,  and  have  not  attempted  to  com- 
bine with  this,  within  the  limits  of  a  single  course  of  lectures, 
the  large  mass  of  facts  and  theories  in  regard  to  the  anatomy 
of  the  central  nervous  organs  which  has  increased  so  rapidly 
during  the  past  few  decads.  In  a  well-arranged  college  course 
students  should  have  acquired  and  digested  this  anatomic 
knowledge  before  commencing  the  study  of  nervous  diseases. 

It  is  most  desirable,  it  seems  to  me,  that  this  change  which 


xKvi  INTRODUCTION. 

has  partially  taken  place  in  the  medical  colleges  should  occur 
also  in  the  text-books,  so  that  these  last  may  devote  their 
entire  space  to  pathology,  as  their  title  implies,  and  not  be 
burdened  by  a  necessarily  somewhat  cursory  description  of  the 
anatomy  of  the  central  nervous  organs,  the  importance  of  which 
is  so  great  that  every  student  of  neurology  should  possess  a 
book  devoted  exclusively  to  its  harmonious  and  complete  expo- 
sition. There  seems,  therefore,  to  be  room  for  an  English  work 
which  shall  present  the  anatomy  of  the  central  nervous  organs 
systematically  and  thoroughly ;  wdiich  shall  begin  with  the 
simplest  elements  and  proceed  to  their  most  complex  combina- 
tion in  these  intricate  organs  without  getting  beyond  the  grasp 
of  the  undergraduate  student,  and  yet  shall  be  complete  enough 
to  satisfy  the  demands  of  the  neurologist. 

Since  the  separation  in  the  teaching  of  the  anatomy  and  of 
the  pathology  of  the  nervous  system  took  place  in  the  Albany 
Medical  College,  Doctor  Gordinier  has  been  in  full  charge  of 
the  instruction  in  the  anatomic  part  of  the  subject,  and  this 
book  is  the  fruit  of  years  of  teaching,  and,  therefore,  should, 
and  I  believe  does,  possess  the  two  characteristics  so  desirable 
in  teaching — clearness  of  style  and  profuseness  of  illustration. 

Henry  Hun. 

Albany,  y////t-  6,  rSgg. 


THE 

GROSS  AND  MINUTE  ANATOMY 

OF   THE 

CENTRAL  NERVOUS  SYSTEM. 


CHAPTER    I 


THE  HISTOLOGIC  ELEMENTS  OF  THE  NERVOUS 

SYSTEM. 

The  histologic  elements  comprise  nerve-cells,  nerve-fibers,  and 
end  organs,  neuroglia  tissue,  blood-  and  lymphatic  vessels,  and 
lymph-spaces. 

HISTOLOGY  OF  THE   NERVE-CELL. 

The  nerve-cell — known  also  under  the  various  names  of  nerve 
vesicle,  corpuscle,  or  ganglion  cell — is  the  beginning  of  a  nerve 
unit,  or  neurone. 

This  unit,  or  neurone,  consists  of  a  cell-body  with  its  various 
protoplasmic  branches,  one  of  which  becomes  a  central  or  per- 
ipheral nerve. 

The  nerve-cell  is  a  granular  protoplasmic  body  containing  a 
large,  usually  centrally  placed,  clear  nucleus,  in  which  lie  one  or 
more  nucleoli.  The  nucleus  is  surrounded  by  a  delicate  mem- 
brane, and  consists  of  a  network  which,  because  of  its  affinity 
for  staining  with  different  reagents,  is  called  chromoplasm,  and 
of  a  more  fluid  material  in  the  meshes  of  the  network  called 
karyoplasm.  Many  of  the  cells  in  the  sympathetic  system 
contain    two    or    more    nuclei.      During   life    the    nucleolus    is 

2  17 


i8  CENTRAL  NERVOUS  SYSTEM. 

usually  angular,  provided  with  processes,  and  capable  of  motion. 
After  death  the  nucleolus  is  highly  refractive,  and  assumes  a 
spheric  form.  The  cells  of  the  central  nervous  system  have  no 
enveloping  membrane  or  capsule,  but  many  of  the  cells  of  the 
peripheral  sympathetic  ganglia,  and  the  ganglia  of  the  posterior 
spinal  nerve-roots,  have  membranous  envelopes  continuous  with 
the  sheaths  of  the  nerves. 

If  a  nerve-cell  is  stained  after  the  method  of  Nissl, — i.e.,  with 
methylene-blue  or  magenta  red, — and  is  examined  with  a  high 
power  of  the  microscope  (xV  oil  immersion),  the  protoplasm  sur- 
roundinfr  the  nucleus  will  be  seen  to  consist  of  a  stainable  and 
an  unstainable  portion.  The  stainable  portion,  which  stains  very 
intensely,  is  composed  of  a  number  of  granular  bodies  separated 
from  one  another  by  parts  of  the  clear  unstainable  portion,  which 
appears  as  a  matrix  in  w^hich  these  granular  bodies  rest.  Each 
Nissl  body  consists  of  a  number  of  very  fine  chromatic  granules, 
held  together  by  a  very  delicate  coagulable  achromatic  substance 
of  unknown  nature.  These  bodies  are  somewhat  irregular,  and 
differ  as  to  size  and  shape:  some  are  oval  or  round,  others 
assume  the  form  of  a  wedge  or  spindle,  while  others  are  rod-like. 
The  nucleus  is  frequently  covered  at  each  end  or  pole  by 
granular  masses  of  like  nature,  called  nuclear  caps.  These 
granular  bodies  are  often  called  the  granules  of  Nissl,  because 
this  observer  discovered  a  very  unique  method  of  staining  them, 
by  means  of  which  they  can  easily  be  recognized  and  studied. 
They  have  the  appearance  of  being  arranged  somew^hat  concen- 
trically in  layers,  starting  from  the  center  and  growing  more 
numerous  as  they  approach  the  periphery.  They  are  called 
protoplasmic  or  chromophyllic  granules,  because  of  their  affinity 
for  the  basic  anilin  dyes.'-" 

Nissl,  from  the  study  of  the  relation  that  the  nerve-cell  body 
bears  to  its  nucleus,  has  divided  nerve-cells  into  two  chief 
groups.  The  first  group  comprises  the  somatochrome  nerve- 
cells,  or  those  cells  w^hose  protoplasm  completely  surrounds  the 


*These  chromophyllic  bodies  also  exist  in  the  dendritic  or  protoplasmic  processes  of  the  cell, 
where  they  are  lengthened  and  appear  rod-like,  presenting  a  faint  longitudinal  striation.  The 
axone,  or  axis-cylinder,  and  the  adjacent  portion  of  the  cell-body  from  which  the  axone  springs, 
called  the  axone  hillock,  is  entirely  free  from  these  granules. 


^fe 


%jal£^    i 


\ 


Fig.   I. — A  Group  of  Multipolar   Nerve-cells   from  an   Anterior   Horn   of  the 
Spinal  Cord.     Showing  Nissl  granules  and  pigment. 

19 


THE   HISTOLOGIC   ELEMENTS   OF   THE   NERVOUS   SYSTEM.  21 

nucleus,  and  has  a  definite  arrangement,  thus  giving  most  prom- 
inence to  the  cell-body.  Most  of  the  nerve-cells  of  the  central 
nervous  system  belong  to  this  group.  The  cells  may  have  their 
chromophyllic  particles  arranged  in  a  network,  when  they  are 
termed  arkyochrome  nerve-cells ;  or  they  may  be  arranged  in 


Fig.  2. — Multipolar  Nerve-cells   from   the   Spinal  Cord   of   an   Ox.     Stained  with 
methylene-blue  and  showing  striation  of  cell-bodies  and  their  processes. 


Striae  which  have  the  same  direction,  appearing  as  if  continuous 
with  one  another,  producing  a  fibrillated  arrangement  to  the 
cell-body,  the  so-called  stichochrome  nerve-cells  ;  or  the  chromo- 
phyllic particles  of  the  cell-body,  may  present  a  combination  of 
both  the  striated  and  network-like  arrangements,  when  they  are 
called    arkyostichochrome    nerve-cells  ;    or,   lastly,   the   chromo- 


22  CENTRAL   XKRVOUS   SYSTEM. 

phyllic  particles  of  the  cell-body  may  consist  of  fine  s^ranules 
and  have  a  definite  arrangement ;  these  are  the  gyrochrome 
nerve-cells. 

The  second  group  consists  of  nerve-cells  in  which  the  cell- 
body  has  no  distinct  form,  the  nucleus  being  the  most  prom- 
inent part  of  the  cell.  This  condition  of  the  cell  is  probably  due 
to  a  lack  of  chromophyllic  particles  and  to  an  increase  of  the 
unstainable  portion.  In  this  group  there  are  two  varieties  :  the 
cytochrome,  or  those  nerve-cells  whose  bodies  are  very  small  in 
comparison  to  their  nuclei,  which  are  about  the  size  of  an  ordi- 


FiG.  3. — A  Ganglion  CiiLi.  kkom  an  Anterior  Horn  ok  the  Si-inal  Cord  ok  an  Ox. 
Showing  the  arrangement  of  the  Nissl  granules  and  the  ramification  of  the  dendrites. 


nary  white  blood-corpuscle  ;  and  the  karyochrome,  or  those 
nerve-cells  whose  bodies  are  very  small,  but  their  nuclei  equal  in 
size  the  nuclei  of  ordinary  nerve-cells. 

It  may  be  of  interest  to  state  that  w^hen  structural  alterations 
occur  in  nerve-cells,  these  changes  are  at  first  shown  in  the 
chromophyllic  bodies  and  appear  as  alterations  of  form,  size, 
position,  and  behavior  tow^ard  staining  reagents.      Lenhossek  '•' 


*  Von  Lenhossek  has  designated  these  granular  Nissl  bodies  tigroid,  from  the  Greek  Tf}jto- 
eM/g,  spotted,  from  the  spotted  appearance  they  give  to  the  cell. 


THE   HISTOLOGIC   ELEMENTS   OF    THE   NERVOUS   SYSTEM.  2j 

States  that  in  no  other  cells  of  the  body  do  granules  exist  having 
the  foreeoingr  characteristics. 

Benda  does  not  support  this  statement  of  Lenhossek,  He 
says  that  similar  bodies  exist  in  gland-cells,  liver-cells,  cells  of 
the  pancreas,  and  in  the  cells  of  some  sarcomatous  tumors. 

In  nearly  all  of  the  cells  of  the  spinal  cord  and  in  many  of  the 
cortical  brain-cells,  particularly  the  large  ganglion  cells  of  the 
latter,  exist  granular  masses  of  yellowish  pigment.  These 
masses  of  pigment  are  frequently  found  close  to  the  giving  oft^ 
of  the  axis-cylinder,  and  sometimes  extend  into  that  process 
and  rarely  into  some  of  the  dendritic  branches  of  the  cell.  This 
pigment,  although  apparently  consisting  of  small  granules,  must 
differ  chemically  from  the  chromophyllic  bodies  of  the  cell, 
because  it  does  not  ordinarily  take  any  staining  reagent  which 
stains  the  protoplasmic  granules.  When,  however,  structural 
alterations  in  the  cell  occur,  the  pigment  is  increased  in  amount 
and  will  stain  a  deep  black  with  osmic  acid. 

Max  Schultze,  about  thirty  years  ago,  discovered  that  each  axis- 
cylinder  of  a  nerve-cell  was  made  up  of  a  number  of  longitudinal 
fibrillae,  which  were  continuous  with  the  fibrillae  that  exist  in  the 
nerve-cell  and  in  its  protoplasmic  branches.  This  observation  of 
Schultze  has  been  entirely  ignored,  until  verified  by  the  recent 
histologic  studies  of  Becker,  Flemming,  Benda,  Marinesco, 
Dogiel,  Nissl,  and  Lugaro.  These  observers  have  found  that  in 
the  unstainable  portion  of  the  cell-body  exist  numbers  of  fine 
fibrillae,  which  extend  into  and  terminate  in  the  ultimate  ramifi- 
cations of  the  dendritic  processes  and  are  continuous  with  the 
fibrillse  of  the  axis-cylinder.* 

*  Gowers'  theory  of  the  conduction  of  nervous  impulses  is  based  upon  the  recent  concep- 
tion of  the  neurone  and  upon  the  histologic  construction  of  nerve-cells  and  fibers  as  described 
long  ago  by  Alexander  Schultze  and  recently  confirmed  by  Becker,  Flemming,  Marinesco,  and 
Dogiel.  He  believes  that  the  fibrillse,  which  have  their  origin  in  the  terminal  ramifications  of 
the  dendrites  and  vsrhich  pass  uninterruptedly  through  the  cell,  conduct  nerve  impulses  through 
that  body,  the  impulses  having  come  from  the  surrounding  collaterals  or  axones,  through  the 
matrix  or  ground  substance  in  which  the  cell  and  its  dendrites  rest.  According  to  this  theory 
the  nerve  impulses  are  merely  in  transit,  the  cell  taking  no  part  in  their  production.  Whether 
or  not  the  matrix  in  vifhich  the  cell-body  and  dendrites  rest,  and  in  vi^hich  the  terminations  of 
collaterals  and  axones  occur-,  simply  transfers  impulses  from  nerve  terminals  to  the  fibrils  in  the 
dendrites  of  the  cell,  or  vi^hether  it  has  anything  to  do  w^ith  the  excitation  of  nerve  impulses, 
is  still  an  open  question.  The  only  function  assigned  to  the  cell  is  trophic  in  character,  the 
nutrition  of  the  cell  processes  being  dependent  on  the  cell-body,  this  nutritional  influence  prob- 
ably coming  from  the  nucleus  of  the  cell. 


24 


CKNTRAL   NKRVOl'S  SVSTK.M. 


FORMS    OR   VARIETIES    OF    NERVE-CELLS. 

The  bipolar  cells  are  found  in  the  ganglia  of  the  sympathetic 
system,  in  the  posterior  spinal  ganglia,  and  ganglia  of  the  sen- 
sory cranial  nerves  in  embryonic  life,  and  in  the  molecular  layer 
of  the  cerebral  cortex.  They  are  spindle  or  pyriform  in  shape, 
and  have  a  single  fine  axone  springing  from  each  pole. 

The  nniltipolar  nerve-cells 
are  very  irregular  masses. of 
protoplasm  having  a  variety 
of  shapes  :  stellate,  angular, 
pyramidal,  caudate,  polygo- 
nal, and  the  like.  They 
are  the  largest  of  all  the 
cells  of  the  nervous  sys- 
tem, varying  in  diameter 
from  eight  to  one  hundred 
and  twenty  //,  the  largest 
being  about  sixteen  times 
the  size  of  a  red  blood- 
corpuscle.  They  possess  a 
large,  clear  nucleus  with  a 
nucleolus,  and  they  usually 
contain  masses  of  yellowish 
pigment.  They  give  off  from 
various  angles  of  the  cell- 
body  numerous  fine,  tubular 
protoplasmic  processes  or 
dendrites,  which  divide  and 
subdivide  like  the  branches 
of  a  tree.  They  are  found 
throughout  the  entire  nervous  system,  but  predominate  in  the 
following  localities — viz.,  in  the  anterior  horns  of  the  spinal  cord, 
in  the  medulla  oblongata,  in  the  cortex  cerebri,  basal  ganglia, 
and  in  the  peripheral  ganglia  of  the  sympathetic. 

There  exist  other  forms  of  nerve-cells,  probably  transitional 
in  character,  among  which  may  be  mentioned  the  so-called  gran- 
ular cells,  which  form  a  distinct  variety  in  many  situations;  as  for 


Fig.  4. — Section  ok  Posterior  Spinal  Gang 
LION  OF  Embryo  Chick.  Illustrating  bi- 
polar cells. — {After  V(7>t  Ge/iuc/i/c-n.) 


THE    HISTOLOGIC    ELEMENTS   OF    THE    NERVOUS    SYSTEM. 


25 


example  :  the  cells  of  the  substantia  gelatinosa  Rolandi  of  the 
posterior  horns  of  the  spinal  cord,  in  the  retina,  olfactory  bulb 
(the  character  of  the  small  cells  which  compose  the  granular 
layer  of  the  olfactory  bulb  is  still  much  in  dispute  ;  Cajal  believes 
them  to  be  nerve-cells,  while  Van  Gehuchten  and  Koelliker  think 
they  are  neuroglia),  and  in  the  cerebellum,  where  they  form  a 
distinct  layer.  Their  protoplasm  is  scant,  and  their  processes 
are  very  difficult  to  discern  with  the  ordinary  methods  of  stain- 
ing.    They  are  probably  bipolar  cells. 


Fig.  5. — MicROPHOTOGRAPH  OF  A  Group  OF  Multipolar  Nerve-cells  from  the  Ante- 
rior Horn  of  the  Human  Spinal  Cord.     Stained  with  the  Cox-Golgi  method. 


PURKINJE   CELL. 

Another  characteristic  form  of  nerve-cell  is  the  so-called 
Purkinje  cell,  found  in  the  cortex  of  the  cerebellum,  where  they 
form  a  distinct  layer.  They  are  quite  regular  in  outline,  some- 
what flattened,  and  distinctly  flask-shaped.  They  are  from  thirty 
to  seventy  p.  in  their  longest  diameter,  and  contain  a  large, 
spheric  nucleus,  "  ten  to  fifteen  ,«  in  diameter,"  with  a  distinct 


26 


CENTRAL   NKRVOUS  SYSTKM. 


nucleolus.  They  are  situated  in  the  cortex  of  the  cerebellum, 
between  the  external  or  molecular  layer  and  the  internal  or 
L^ranular  layer.  From  their  basal  surface  proceeds  a  distinct 
slender  axis-cylinder  process  of  great  length,  which  continues 
downward  through  the  granular  layer  into  the  medullary  por- 
tion or  white  matter,  where  it  becomes  a  medullated  nerve-fiber. 
In  its  course  it  gives  off  collaterals  which  curve  upward  and  ter- 


«► 


«     %■ 


Fig.  6. — Microphotograi'h  showing  Purkinje  Ckli.. 


minate  in  the  external  or  molecular  layer.  From  the  opposite 
or  cortical  end  of  the  cell-body  spring  two  processes,  or  den- 
drites, or  a  single  process  which  soon  divides  into  two,  and  this 
dichotomous  division  continues  until  an  enormous  tree-like  mass 
of  fibers  is  produced,  which  covers  a  considerable  extent  of  sur- 
face and  is  always  distinct  from  the  branching  processes  of  other 
cells. 


THE   HISTOLOGIC   ELEMENTS   OF   THE   NERVOUS   SYSTEM.  27 


£f- 


Gl 


Fig.  7. — A  Frontal  Section  through  an  Olfactory  Bulb  of  a  Six-weeks' -old  Cat. 

Showing  layer  of  granular  cells. — (^After  Koelliker.^ 
Ep.  Ependyma.      Gl.   Glomerule.     Kz.   Layer  of  granular  cells.     M.   Molecular  layer.     MF. 

Layer  of  medullated  fibers.     MZ.   Layer  of  mitral  cells.     Str.  gr.   Granular  zone  (stratum 

granulosum). 


28 


CENTRAL   NERVOUS  SYSTEM. 


THE  BASKET  CELL  OK    TMH  CEREBELLU^L 

This  is  a  cell  peculiar  to  the  cerebellar  cortex,  the  axone  or 
nerve  process  of  which  has  a  horizontal  course,  and  continually 
o-ives  off  descending  collateral  branches  which  terminate  in 
brushes  of  fibrils  about  the  bodies  of  the  Purkinje  cells,  giving 
them  the  appearance  of  resting  in  a  basket  of  tine  tibrils. 


Fig.  8. — Microphotoc-.raph  ok  Small  Pyramidal  Cells. 


PYRAMIDAL  CELLS  OF  THE  CORTEX. 

The  pyramidal  cells  of  the  cerebral  cortex  are  so  numerous 
and  of  such  anatomic  and  physiologic  importance  that  they  may 
well  be  described  separately.  They  properly  belong  to  the 
multipolar  variety  of  cells,  are  triangular  or  pyramidal  in  shape, 
and  possess  a  fine  apical  dendrite  or  process  which  gradually 
tapers  as  it  extends  toward  the  superficial  layer  of  the  cortex. 
Many  of  these  apical  processes  bifurcate  close  to  their  cortical 
ending.      Delicate  protoplasmic  processes  or  dendrites  project 


THE    HISTOLOGIC    ELEMENTS    OF    THE    NERVOUS    SYSTEM. 


29 


from  all  parts  of  the  cell-body,  while  from  each  corner  of  the 
base  springs  a  dendrite  which  extends  obliquely  to  the  plane  of 
the  vertical  fibers  of  the  cortex,  and  divides  into  numerous 
irregular  branching  filaments,  all  of  which  are  studded  in  their 
course  by  minute  protoplasmic  offshoots,  the  so-called  gemmules 
or  buds.  These  buds  or  gemmules  are  minute  in  diameter 
where  they  join  the  dendritic  branch,  grow  larger,  and  terminate 
in  a  beaded  extremity.  They  are  also  found  on  the  apical 
branches   of   the   cell.     They  probably  serve  to  convey  nerve 


Fig.  9. — MrcKOPHOTOGRAPH  of  Large  Pyramidal  Cells. 


impulses  from  one  dendrite  to  another,  or  receive  impulses  from 
the  intracortical  end-apparatus  (Berkley).  The  axis-cylinder 
process  generally  springs  from  the  middle  of  the  basal  portion 
of  the  cell-body,  passes  vertically  downward,  is  usually  of  great 
length,  smooth,  less  in  diameter  than  the  dendrites,  and  gives  off  at 
right  angles  collateral  branches.  Each  cell  contains  an  oval  nu- 
cleus with  well-defined  nucleolus,  and  varies  from  eig-ht  to  twelve 
//  in  diameter.  The  larger  ones  are  called  the  giant  pyramidal 
cells  (Betz),  and  are  probably  motor  in  function.     Some  of  these 


30 


CENTRAL  NERVOUS  SYSTEM. 


cells,  accordini^-  to  Bevan  Lewis,  measure  thirty  to  ninety-six  //  in 
length  and  twelve  to  forty-five  //  in  breadth.  This  variety  of 
cell  nearly  always  contains  an  al)iindance  of  yellowish  pigment. 


~N,. 


*^^^^**»s--. 


Fig.   io. — A  Group   ok    Large  Pyramidal   Cells   from  the  Motor  Area   of   the 
Human  Brain.     Stained  after  the  method  of  Bevan  Lewis. 


CELL  PROCESSES  AND  NERVE-FIBERS. 
The  protoplasmic  body  of  the  cell  gives  off  from  projections 
on  its  surface  a  number  of  processes  which  branch  out.  tree- 
like, in  all  directions  and  divide  into  filaments  of  extreme  fine- 


THE   HISTOLOGIC   ELEMENTS   OF    THE  NERVOUS  SYSTEM.  31 

ness.  Some  of  them  are  very  long,  while  others  are  short  and 
thick.  These  branches,  or  dendrites,  as  they  are  termed,  do  not 
anastomose  with  one  another  or  with  adjacent  or  distant  cell 
branches,  but  may  influence  other  dendrites  or  nerve  processes 
by  near  approximation  or  slight  contact. 

By  connecting  with  blood-vessels  and  lymphatics,  they  may 
serve  a  nutritional  function  (Golgi).  Most  observers,  however, 
believe  that  they  have  a  nervous  function,  collecting  nerve  im- 
pulses from  nerve-cell  processes  and  conveying  them  to  their 
own  cell-body. 

The  Axis-cylinder. — The  most  important  process  of  the 
cell  is  the  axis-cylinder  process,  known  also  under  the  name 
of  neuraxone,  axone,  or  nervous  process.  Along  this  process 
travel  nervous  impulses  to  or  from  the  cell-body.  It  is,  there- 
fore, the  conducting  medium  for  nervous  impulses  originating 
from  the  periphery  and  passing  centrally,  or  vice  versa.  This 
process  is  always  single  except  from  the  cells  in  the  uppermost 
cortical  layer  of  the  cerebrum  and  in  the  cells  of  the  spinal 
and  sympathetic  ganglia  and  ganglia  of  the  sensory  cranial 
nerves.  The  cells  of  the  posterior  spinal  ganglia  in  man  have 
been  incorrectly  described  by  many  authors  as  belonging  to  the 
bipolar  type.  This  description  is  true  insomuch  as  it  applies  to 
the  lower  vertebrates.  In  man,  however,  this  bipolar  type  is 
seen  only  in  fetal  life.  As  development  goes  on,  the  two  axones 
either  become  fused  in  their  entirety,  forming  one  axone,  which 
branches  T-shaped,  or,  what  seems  more  probable,  there  is  an 
unequal  development  of  the  cell-body  to  form  a  protoplasmic 
pedicle  from  which  the  branching  axone  takes  its  origin.  The 
axone  starts  as  a  delicate  single  strand  of  protoplasm,  variable  in 
length,  which  frequently  gives  off  a  few  lateral  branches  (collat- 
erals). In  most  cases  it  receives,  soon  after  leaving  the  cell 
body,  a  layer  of  myelin,  and  becomes  a  medullated  nerve-fiber. 


NERVE-FIBERS. 

There  are  two  chief  forms  of  nerve-fibers,  the  white  and  the 
gray — the  medullated  and  the  non-medullated. 

The  white  or  the  medullated  nerve-fibers  form  the  white  sub- 


32 


CEXIKAL    NERVOUS  SVSl'KM. 


Stance  of  the  cerebrospinal  system  antl  the  greater  part  ot  tlie 
peripheral  nerves,  and  give  to  them  their  characteristic  micro- 
scopic and  macroscopic  appearance.  Each  fiber  consists  of  a 
central  portion  or  core, — the  axis-cylinder  of  Purkinje,  which  is 


Fig.  II. — Xervk-fibers  iro.m  the  Muscle  of  a  Frog  Injected  with  Methylene- 
KLUE.  Showing  the  dark  stained  axis-cylinders,  the  nodes  of  Ranvier,  and  the  separation 
of  the  terminal  axones  into  several  primitive  librillse. — (.-//?<■/■  Koi'lliker.^ 


the  essential  part  of  the  nerve  and  conducts  nervous  impulses. 
This  axis-cylinder  is  longitudinally  striated,  due  to  the  fact  that 
it  consists  of  a  number  of  exceedingly  fine  fibrillae,  which  are 
arranged  longitudinally  and  are  held  together  by  a  very  deli- 


THE   HISTOLOGIC   ELEMENTS   OF   THE   NERVOUS   SYSTEM. 


33 


cate  stroma  or  network  called  by  Koelliker  "neuroplasm,"  and 
by  Waldeyer  "  axioplasm."  At 
the  termination  of  a  nerve-fiber 
the  axis-cylinder  often  separates 
into  a  number  of  terminal  fila- 
ments, which  are  termed  the  primi- 
tive fibrillae  of  Max  Schultze  (Fig. 
ii).*  Near  the  nodes  of  Ranvier 
it  is  not  uncommon  to  find  trans- 
verse markings  in  the  axis-cylin- 
der. These  are  the  so-called  lines 
ofFrohmann.     Each  axis-cylinder 


sJi       ^H 


Fig.  12. — Medullated  Nerve-fibers 
Blackened  by  Osmic  Acid. — [La7i- 
dois  and  Stirling.) 

fs.   Ranvier' s  node.     sch.  Schwann's 
sheath. 


Fig.    13. — Medullated  Nerve-fibers 
(with  Osmic    AcidJ. — [Landois  and 
Stirling. ) 
a.  Axis-cylinder.      s.   Sheath    of  Schwann. 
n.  Nucleus.     /,  p.  Granular  substance  at 
the  poles  of  the  nucleus,     r,  r.  Ranvier's 
nodes,    where    the    medullary   sheath    is 
interrupted  and  the  axis-cylinder  appears. 
/,  i.   Incisures  of  Schmidt. 


is  the  prolonged  axone  of  a  nerve-cell,  and  remains  uninter- 


*The  fibrils  composing  the  axone  consist  of  a  conduciing  medium  called  by  Hansen  "  hya- 
loplasm," and  a  granular  material  called  "  spongioplasm."  Gowers  calls  the  terminal  fila- 
ments of  the  axis-cylinder  "axites." 


34 


CENTRAL  NERVOUS  SYSTEM. 


rupted  throughout  its  course.  It  is  surrounded  by  a  dehcate 
sheath  composed  of  a  substance  similar  to  horny  material,  hence 
called  neurokeratin.  This  sheath  is  called  the  axilemma.  Sur- 
rounding the  axis-cylinder  is  a  layer  of  semifluid  fatty  material 
which  stains  deep  black  with  osmic  acid,  called  myelin  ;  or,  from 
its  discoverer,  the  white  substance  of  Schwann.      Tlie  myelin 

has  an  inner  and  an  outer  layer  of  neuro- 
keratin, with  an  intervening  network  of 
the  same  material,  in  the  meshes  of 
which  exist  the  droplets  of  semifluid 
myelin.  Owing  to  its  peculiarity  of  re- 
fraction the  myelin  gives  to  the  nerve- 
fiber  as  seen  with  transmitted  light  its 
double  contour  (Figs.  12  and  13). 

The  myelin,  or  white  substance  of 
Schwann,  apart  from  giving  to  the  nerve- 
fiber  its  contour,  is  a  protective  to  the 
axis-cylinder,  and  possibly  may  act  as 
a  non-conducting  medium  to  prevent 
nervejmpulses  from  being  deflected  from 
their  intended  course.  It  does  not  form 
a  continuous  envelop  for  the  axis-cylin- 
der, but  at  rather  regular  intervals  it  is 
interrupted,  leaving  gaps  or  constrictions 
called  Ranvier's  nodes.  The  nerve  seg- 
ment between  two  nodes  is  called  an 
interannular  or  internodal  segment.  The 
internodes  are  united  within  the  sheath 
of  Schwann  by  the  constricting  bands 
of  Ranvier,  a  sort  of  annular  rincr  formed 
of  an  albuminous-like  material.  This 
material  stains  readily  with  silver  nitrate,  which  agent  also 
stains  the  axis-cylinder  at  the  nodes,  producing  the  so-called 
crosses  of  Frohmann  (Fig.  14).  Each  internodal  segment  con- 
tains just  below  its  middle  an  oval-shaped  nucleus  situated 
beneath  the  covering  of  the  myelin  or  neurilemma  in  a  depres- 
sion of  the  myelin.  The  nodes  of  Ranvier  are  supposed  to 
subserve  a  nutritive  function,  permitting  the  passage  of  blood 


Fig.  14. — A  Bunui.k  ok 
Nerve-fibers  Stained 
WITH  Nitrate  of  Silver. 
— {After  Ranvier.^ 

Showing  the  outlines  of  epi- 
thelial cells  of  the  perineu- 
rium. The  dark  crosses  of 
Frohmann  on  the  nerve-fibers 
at  the  nodes  of  Ranvier  are 
due  to  the  staining  of  the 
axis-cylinder  and  of  a  band 
of  intercellular  substance 
which  encircles  the  axis-cyl- 
inder at  the  node. 


THE  HISTOLOGIC   ELEMENTS   OF    THE   NERVOUS   SYSTEM.  35 

plasma  Into  the  axis-cylinder.  Certain  incisures  can  be  seen 
in  the  myelin  which  extend  obliquely  across  it.  These  are 
named,  from  their  discoverers,  the  incisures  of  Schmidt  or 
Lantermann.  By  many,  and  particularly  Koelliker,  they  are 
considered  as  artifacts,  the  latter  observer  never  having  found 
them  in  living  nerves. 

It  has  been  shown  that  the  layer  of  myelin  which  surrounds 
most  of  the  nerve-fibers  of  the  central  nervous  system  appears 
for  the  various  tracts  at  different  periods  of  fetal  development. 
Flechsig  has  shown  that  fibers  which  have  the  same  function 
develop  simultaneously,  and  in  the  direction  in  which  they  con- 
duct impulses. 

Surrounding  the  myelin,  or  white  substance  of  Schwann, 
is  a  closely  investing,  delicate,  almost  structureless  membrane, 
called  the  neurilemma,  primitive  or  tubular  sheath  of  Schwann. 
This  sheath  is  continuous  and  uninterrupted  throughout, 
although  it  presents  constrictions  which  correspond  to  the 
nodes  of  Ranvier,  which  dip  down  almost  to  the  axis-cylinder. 
Some  medullated  fibers  lack  this  sheath  of  Schwann,  or  neuri- 
lemma, being  simply  inclosed  in  myelin  ;  as,  for  example, 
the  white  fibers  of  the  brain  and  columns  of  the  spinal  cord. 
The  size  of  medullated  fibers  varies  very  much,  this  being  due 
mainly  to  the  amount  of  myelin  surrounding  them,  although 
the  axis-cylinders  also  vary  in  diameter.  The  diameter  of  the 
axis-cylinder  depends  somewhat  upon  the  cell  from  which  it 
springs  and  upon  the  length  of  its  course,  the  large  cells  usually 
giving  off  nervous  processes  of  greater  diameter  and  length 
than  those  from  smaller  cells.  The  medullated  nerves  vary 
from  2  to  2.5  [J.,  or  ttoo  to  toito  of  an  inch,  in  diameter. 

Non-medullated  Fibers. — These  fibers  occur  chiefly  in  the 
sympathetic  system,  and  are  sometimes  called  sympathetic  or 
Remak's  fibers.  These  non-medullated  fibers  differ  in  form. 
First,  simple  nerve  strands  presenting  globose  swellings  are 
found,  occurring  near  the  termination  of  nerve-fibers,  being 
formed  by  the  splitting-up  of  their  axis-cylinder  processes — as, 
for  example,  the  optic  nerve  layer  of  the  retina,  the  ramifications 
of  the  olfactory  nerves,  and  as  is  often  seen  among  the  fibers  of 
the  spinal  cord  and  brain.     Secondly,  as  naked  axis-cylinders, 


36 


CENTRAL  NERVOUS  SYSTEM. 


which  are  primitive  fibers  held  together  by  a  cement  substance — 
as,  for  example,  the  axis-cylinder  processes  of  many  nerve-cells. 
Thirdly,  axis-cylinders  surrounded  by  a  very  delicate  sheath, 
which  corresponds  to  the  neurilemma  or 
Schwann's  sheath  of  medullated  nerves. 
These  fibers  bear  the  name  of  Remak,  their 
discoverer,  and  are  commonly  described  as 
the  non-medullated  fibers  of  the  sympathetic 
system,  or  the  fibers  of  Remak  (Fig.  15). 
They  contain  nuclei  situated  at  intervals  in 
each  fiber  lying  between  the  axis-cylinder  and 
neurilemma,  and  are  faintly  striated. 

This  form  is  found  in  the  sympathetic  sys- 
tem and  in  some  of  the  cranial  nerves.  All 
nerves  of  the  embryo  up  to  a  certain  period 
of  development  are  also  of  this  kind. 

The  size  of  the  non-medullated  fibers 
varies,  these  being  in  general  about  half  the 
size  of  the  medullated  fibers  ;  but  some — as, 
for  example,  those  of  the  olfactory  bulb — 
are  many  times  the  size  of  the  medullated 
fibers. 

The  nerve-fibers  are  joined  into  fasciculi 
or  bundles  by  a  connective-tissue  sheath. 
These  bundles  are  in  turn  united  to  other 
bundles,  to  form  a  peripheral  nerve.  The 
sheath  which  unites  and  covers  the  nerve 
bundles  or  fasciculi  is  called  the  epineurium 
(Fig.  16).  It  serves  to  convey  to  the  nerve 
bundles  blood-vessels,  lymphatics,  and  nerves. 
The  connective-tissue  sheath  which  encircles 
each  individual  bundle  or  fasciculus  is  covered 
by  epithelium,  and  from  its  position  is  called 
the  perineurium.  The  delicate  sheath  which  is 
between  the  fibers  of  each  single  fasciculus  is  termed  the  endo- 
neurium.  It  serves  to  give  support  to  the  nerves  and  blood-ves- 
sels, and  communicates  by  channels  with  the  lymphatics  of  the 
perineurium.     The    nerve  trunks    themselves   are  supplied  by 


Fig.  15. — Remak's  Fi- 
ber FROM  Vagus  of 
Dog. — {^Landois  and 
Stirling. ) 

b.  Fibrils,  n.  Nucleus. 
/.  Protoplasm  sur- 
rounding it. 


THE   HISTOLOGIC   ELEMENTS   OF   THE   NERVOUS   SYSTEM. 


37 


nerve-fibers  which  extend  through  the  epineurlum,  terminating 
in  end  bulbs.  These  are  the  nerves  of  the  nerve,  or  the  nervi 
nervorum. 

The  nerve  centers  of  the  cerebrospinal  axis  are  supported  by 
connective-tissue  envelopes,  connective  tissue  about  the  blood- 
vessels, and,  most  important  of  all,  a  neuroglia  tissue  matrix. 


THE  PERIPHERAL  NERVE  TERMINATIONS. 

The  peripheral  nerves,  which  contain  mixed  motor  and  sensory 


Fig.  i6. — TRANb\  erse  Section  of  a  Ner\e  (Median)  — {Landus  and  Stirling.^ 
ep.   Epineurium.     pe.   Perineurium,     ed.  Endoneurium. 

fibers,  terminate  in  one  of  three  ways.  First,  in  interepithelial 
arborizations  ;  second,  in  specialized  end  organs  or  tactile  cor- 
puscles ;  and  third,  in  the  motorial  end  plates.  The  first  two 
methods  of  termination  belong  to  the  sensory  nerves  only,  while 
the  last  method  belongs  to  the  sensorimotor  nerves  of  the 
voluntary  muscles.  There  are  six  chief  forms  of  specialized  end 
organs — namely,  the  tactile  corpuscles  of  Meissner  and  Wagner, 
the  end  bulbs  of  Krause,  the  Pacinian  or  Vater's  corpuscles, 
the  tactile  menisques,  the  corpuscles  of  Golgi,  and  the  so-called 
muscle  spindles. 


38 


CENTRAL   NERVOUS  SYSTEM. 


THE  TERMINATIONS  OF  SENSORY  NERVES. 

First,  the  interepithelial  arborizations.     This  is  the  usual  mode 
of  ending-  for  a  large  number  of  sensory  nerves.     They  termi- 


mmm 


Fig.  17. — Ti-.RMiNATioN  OK  Sensory  Nerves  in  Stratified  Squamous  Epitiiki.hm. 
GoLGi  Stain. — {After  Relzius.) 


d  0 

Fig.  18. — Vertical  Section  ok  the  Skin  of  the  Palm 
Of  the  Hand. — {Landois  and  Stirling.) 

a.  Blood-vessels,  b.  Papillaof  the  cutis  vera.  c.  Capillary. 
d.  Nerve-fiber  passing  to  a  touch  corpuscle,  f.  Nerve- 
fiber  divided  transversely,  e.  Wagner's  touch  corpuscle. 
g.  Cells  of  the  Malpighian  layer  of  the  skin. 


Fig.  19. — Wagner's  Touch 
Corpuscle  from  the 
Palm,  Treated  with 
Gold  Chlorid. — [Landois 
and  Stirling. ) 

«.  Nerve-fibers,     a,  a.  Groups 
of  glomeruli. 


THE   HISTOLOGIC   ELEMENTS   OF   THE   NERVOUS   SYSTEM. 


39 


nate  in  the  skin  and  mucous  membranes,  as  well  as  in  the  hair 
bulbs,  the  teeth,  the  tendons  of  muscles,  and  many  of  the  glands 
of  the  body.  As  the  nerve-fiber  approaches  the  surface  of 
the  skin  or  the  mucous  membrane  it  loses  its  myelin  and  neuri- 
lemma. The  naked  axis-cylinder  then  repeatedly  divides,  form- 
ing a  ramified  plexus  of  fine  fibrils,  which  terminate  by  passing 
among  the  epithelial  cells  of  the  skin  and  mucous  membrane 
(Fig.  17). 

Secondly,  the  tactile  corpuscles  of  Meissner  and  Wagner. 
These  touch  corpuscles  are  most  numerous  where  the  sense  of 
touch  is  best  developed, — that  is,  in  the  palms  of  the  hands  and 


Fig.  20. — Cylindric  End  Bulbs  from  the  Conjunctiva  of  the  Calf. — [Merkel.) 
A.   Longitudinal  section.       B.    Transverse  section.       «.    Entering  nerve-fiber.       c.  Nucleated 

capsule. 


soles  of  the  feet,  especially  in  the  ends  of  the  fingers  and  toes, — 
more  sparingly  in  the  tip  of  the  tongue,  skin,  and  lips,  back  of 
the  hands  and  feet,  skin  of  the  nipples,  and  in  the  conjunctiva. 
They  are  oval  or  elliptic  in  shape,  about  seventy  //  or  -^  of  an 
inch  in  length,  and  thirty;/  or  %^-^  of  an  inch  in  thickness  (Figs,  i  7 
and  18).  They  are  composed  of  connective  tissue  consisting  of 
a  capsule  which  sends  numerous  trabeculse  into  its  interior,  which 
serve  to  support  the  nerve-fibers  in  their  spiral  or  convoluted 
course.  Several  medullated  nerve-fibers  pass  to  the  base  of  each 
capsule  and  surround  it  in  a  spiral  manner  ;  they  then  enter  the 
capsule  and  pursue  a  spiral  course,  supported  by  the  trabeculae, 
and  terminate  in  globular  enlargements  close  to  the  capsule. 


40 


CENTRAL  NKRVOUS  SYSTEM. 


THE  END   BULBS  OF  KRAUSE. 

These  are  very  small  cylindric  or  oval-shaped  corpuscles, 
and  are  sligrhdy  bent  near  their  base.  They  are  from  0.075  ^^ 
0.14  mm.  in  diameter.  They  consist  of  a  nucleated  connective- 
tissue  capsule,  in  the  interior  of  which  is  a  core  of  soft  protoplasm 
containing-  numerous  polyhedral  cells,  in  which  rests  the  naked 
axis-cylinder,  the  myelin  being  lost  when  the  latter  enters  the  base 
of  the  capsule  (Figs.  20.  21,  and  22).     Ihe  neurilemma  continues 


Fig.  21. — End  Bulb  of  the  Human  Conjunc- 
Tiv.\,  Treated  with  a  Mixture  of  Acetic 
AND  OsMic  Acids.  — (^  Krause.) 
n.   Two  medullated  nerve-fibers  entering  cor- 
puscle. 


Fig.  22. — Articular  Corpuscle  i-rom 
Phalangeal  Joint  in  Man. — ( IV. 
Krause.) 


inward  with  the  axis-cylinder,  and  forms  a  lining  to  the  capsule 
and  a  covering  for  the  central  protoplasmic  core.  The  axis- 
cylinder  usually  terminates  near  the  extremity  of  the  capsule  in  an 
elongated  globular  expansion.  Rarely  the  nerve-fiber  separates 
into  two  or  three  parts  which  become  twisted  before  terminating. 
These  corpuscles  are  found  in  the  mucous  membranes  of  the 
mouth,  lips,  nose,  and  conjunctiva,  in  the  papillae  of  the  tongue, 
in  the  mucous  membrane  of  the  glans  penis  and  vagina,  and  in 
the  synovial  membranes  of  the  joints  of  the  fingers,  in  which 
latter  place  they  are  often  called  articular  end  bulbs. 


THE   HISTOLOGIC   ELEMENTS   OF    THE   NERVOUS   SYSTEM. 


41 


The  Pacinian  or  Vater's  corpuscles  are  irregularly  oval-shaped 
bodies  situated  on  some  of  the  cerebrospinal  and  sympathetic 
nerves,  and  are  from  ^t  to  tV  of  an  inch  in  length  and  from  23- 
to  To  of  an  inch  in  breadth.     Each  corpuscle  incloses  the  termi- 


■'--.■  '^■'■**\^ 

t  ■.■  '^ 

A 

^-^,- 

. 

•  w  '  ■"■■ 

1 

P 

Fig.  23. — A  Microphotograph   of   two  Pacinian  Corpuscles   from  the   Mesentery 

OF  A  Cat. 


nation  oi  a  single  nerve-fiber,  which,  with  its  connective-tissue 
sheath  and  blood-vessel,  forms  a  pedicle  by  which  the  corpuscle 
is  attached  to  the  main  nerve.  These  bodies  consist  of  a  lami- 
nated connective-tissue  capsule  composed  of  from  forty  to  fifty 
tunics  or  lamellae.     Each  tunic  decreases  in  thickness  from  with- 


42  eEXTRAI.  NERVOLS  SYSTEM. 

out  inward,  and  tlie  several  tunics  are  arranged  similarly  to  the 
coats  of  an  onion.  Each  lamella  consists  of  white  connective- 
tissue  fibers  arranged  transversely,  and  of  elastic  fibers  which 
pass  in  a  variety  of  ways.  The  lamellae  are  lined  with  endothelial 
cells,  and  are  slighdy  separated  from  one  another  by  a  transparent 
fluid,  probably  lymph  (Fig.  23).  In  the  central  part  or  axis  of 
each  corpuscle  is  the  core,  made  of  a  soft  material  (protoplasm)^ 
through  which  passes  the  prolongation  of  the  nerve-fiber.  A 
single  medullated  nerve-fiber  passes  into  each  corpuscle,  the 
sheath  of  Schwann  uniting  with  the  capsule.  The  myelin  is  lost 
and  the  naked  axis-cylinder  proceeds  through  the  soft  central 
core,  to  terminate  near  the  extremity  of  the  capsule  in  a  vari- 
cosity.    Sometimes  the  fiber  forks,  each  division  terminating  in 


/^f 


'To 

Fig.  24. — Tactile  Mknisque  from  the  Nose  of  a  Guineapig. — {Ranvic-r.) 
n.  Nerve-fiber,     a.  Tactile  cells,     iii.  Tactile  discs,     c.   Epithelial  cells. 

an  oval  expansion.  These  corpuscles  are  found  in  the  subcuta- 
neous tissue  on  the  nerves  of  the  fingers  and  toes  in  the  neigh- 
borhood of  joints,  on  the  intercostal  nerves,  the  nerves  of  the 
arms  and  of  the  neck,  on  those  of  the  nipples,  on  those  of  the 
external  genitalia  of  both  sexes,  on  the  nerves  of  the  abdominal 
sympathetic,  and  particularly  on  the  nerves  of  the  mesentery. 
They  are  very  abundant  on  the  nerves  of  the  mesentery  of  the 
cat,  where  they  are  often  so  large  that  they  may  be  seen  with 
the  naked  eye. 

THE  T.ACTILE  MENISQUES. 

Another  form   of  termination  of  the  sensory  nerve-fibers   is 
that  of  the  tactile  menisques  of   Ranvier  (Fig.  24).     They  occur 


THE   HISTOLOGIC   ELEMENTS   OF   THE   NERVOUS   SYSTEM. 


43 


in  both  the  superficial  and  deep  layers  of  the  skin,  and  consist  ot 
plexuses  of  nerve-fibers  which  form  arborizations  whose  branches 
become  flattened,  resembling  leaves  in  shape. 


THE  CORPUSCLES  OF  GOLGI. 

A  special  form  of  muscle  nerve-ending  has  been  described  by 
Golgi  and  Rollett,  and  occurs  in  tendons,  particularly  near  the 
point  of  junction  of  the  tendon  with  the  muscle.  At  that  point 
the  bundles  of  fibers  composing  the  tendon  become  somewhat 
enlarged,  and  meduUated  nerve-fibers,  after  losing  their  myelin, 
penetrate  the  fibers  composing  the  tendon.    They  then,  as  naked 


Fig.  25. — Organ  of  Golgi  from  the  Human  Tendo  Achillis,  Chlorid  of  Gold 

Preparation. — {^After  Ciaccio.) 

f?i.  Muscular  fibers,     t.   Tendon  muscles.      G.    Golgi's  organ,      n.   Nerve-fibers. 


axis-cylinders,  break  up  into  a  number  of  fibrils,  which  form 
terminal  arborizations,  somewhat  spindle  shaped.  This  enlarge- 
ment of  the  fibers  of  the  tendon,  with  the  terminal  arborizations, 
forms  the  so-called  corpuscles  of  Golgi  (Fig.  25). 


THE  MUSCLE  SPINDLE. 


These  bodies  have  been  found  in  nearly  all  the  skeletal 
muscles,  but  are  especially  abundant  in  the  biceps  of  the  arms 
and  in  the  small  muscles  of  the  hands.  They  are  found  more 
abundantly  in  the  belly  of  the  muscle  than  in  the  tendon,  and  are 


44  CENTRAL   NKRVOUS  SYSTEM. 

most  easy  of  demonstration  in  atrophied  muscles.  They  do 
not  occur  or  else  are  very  uncommon  in  the  muscles  of  the 
eye,  the  diaphragm,  and  intrinsic  muscles  of  the  tongue.  They 
vary  from  2  to  4  mm.  in  length  and  0.15  to  0.4  mm.  in  breadth. 
These  bodies,  as  their  name  implies,  are  spindle  shaped.  They 
are  often  found  lying  parallel  to  the  nerve  which  supplies 
them  ;  frequently  two  spindles  will  be  found  in  the  same  plane, 
lying  end  to  end. 

The  muscle  spindle  consists  of  muscle-fibers,  nerves  and 
their  endings,  a  connective-tissue  sheath,  blood-vessels,  and 
lymphatics. 

One  or  more  muscle-fibers,  somewhat  diminished  in  size,  enter 
either  the  distal  or  proximal  pole  of  the  muscle  spindle  and 
pass  toward  the  center  of  the  spindle,  where  they  usually  divide 
into  several  smaller  fibers  ;  they  then  begin  to  lose  their  trans- 
verse markings,  and  become  nucleated,  the  nuclei  completely 
fillinof  the  muscle-fiber.  These  nuclei  exist  for  a  short  distance 
in  the  muscle-fiber  at  the  equatorial  region  of  the  spindle,  after 
which  the  fiber  again  becomes  striated.  Each  spindle  is  usually 
supplied  by  two  nerves,  one  of  which  enters  the  spindle  at  the 
distal  or  proximal  end,  and  one  entering  the  spindle  at  its  cen- 
tral part.  The  nerve-fiber  which  enters  the  spindle  at  its  center 
is  the  larger,  and  probably  terminates  about  the  nuclei  of  the 
muscle-fiber.  The  other  nerve-fiber  forms  a  plexus  of  fibrils 
beneath  or  in  the  sheath  of  the  spindle,  or  else  terminates  in 
bulbous  extremities.  The  nerve  sheaths  blend  w-ith  those  of 
the  muscle  spindle  on  entering  the  latter. 

The  sheath  of  the  spindle  consists  of  several  laminae,  which 
have,  on  cross-section,  the  appearance  of  an  onion.  At  the 
center  of  the  spindle  there  are  from  eight  to  ten  laminae,  but  at 
the  poles  they  become  less  in  number  and  blend  with  the 
sheaths  of  the  muscle.  The  sheath  of  the  spindle  sends  many 
septa  into  the  interior  of  the  spindle,  w^hich  pass  between  the 
muscle-fibers  and  nerves.  The  blood-vessels  of  the  spindle 
usually  enter  and  leave  at  the  opening  for  the  central  nerve. 
A  lymphatic  space  exists  in  the  center  of  each  spindle,  occupy- 
ing about  its  middle  third.  The  function  of  the  muscle  spindle 
is  not  positively  known,  but   from   the  situation  and  important 


THE   HISTOLOGIC   ELEMENTS   OF   THE   NERVOUS   SYSTEM. 


45 


nerve  connection,  it  is  supposed  to  be  concerned  in  the  produc- 
tion and  conveyance  of  muscle-sense  impressions. 


THE  TERMINATIONS  OF  THE  MOTOR  NERA^ES. 

The  motor  nerves  terminate  both  in  voluntary  and  involuntary 
muscles.  In  the  former  the  nerves  are  all  medullated  and  have 
their  origin  in  the  cerebrospinal  system,  while  in  the  latter  they 
are  non-medullated  and  belong  to  the  sympathetic  system.  The 
motor  nerves  to  the  voluntary  muscles  terminate  chiefly  in 
special  expansions  which  have  received  the  various  names  of 
motor  nerve  plates  or  organs,  motor  sprays,  or  fields  of  inner- 


End  plate 


Muscle  nucleus 


T-T  ^  T,      I  V  ' il-^J^'!■3S'SMil|li 

Nerve    — f-  .: 4  <'(  ,    .     v  i  ■■ /'./'li'-iHiiiiilif 

Fig.  26. — Muscular-fibers  with  Motorial  End  Plates. — [Landois  and  Stirlhig 


vations  of  Kuhne,  or  the  eminences  of  Doyere.  These  end 
organs  or  plates  are  located  beneath  the  sarcolemma  of  the 
primitive  muscle-fibers,  and  are  continuous  with  their  sarcous 
substance.  They  are  flattened  or  slightly  elevated  masses  of 
granular  protoplasm  having  an  irregularly  spheric  or  oblong 
shape,  and  contain  cells  with  investing  envelopes  and  clear  oval 
nuclei  and  nucleoli. 

In  mammals  each  individual  muscle-fiber  usually  has  but  one 
end  organ  and  receives  but  one  nerve-fiber.  If  the  muscle- 
fiber  be  especially  long,  more  than  one  nerve-fiber  may  enter  it. 
In  reptiles,  however,  two  or  more  end  organs  are  frequently 
found  in  a  single  muscle-fiber.  Each  motor  nerve-fiber  as  it 
passes  into  the  muscle  repeatedly  divides  at  the  nodes  of  Ranvier 


46  CENTRAL   XKKVOUS  SYSTEM. 

into  a  number  of  branches,  the  courses  of  which  are  both  ascend- 
ing and  descending.  These  in  turn  give  off  a  number  of  fine 
forked  branchlets,  each  of  wliich  pursues  mostly  an  obHque  or 
transverse  course  between  the  muscle-fibers,  forming  an  intra- 
muscular nerve  plexus.  Each  primitive  nerve  fibril  still  medul- 
lated  passes  to  a  muscle-fiber,  having  divided  just  before  reaching 
it.  As  it  enters  the  fiber  it  loses  its  myelin,  and  the  neurilemma 
sheath  becomes  continuous  with  the  sarcolemma  of  the  muscle- 
fiber.  The  naked  axis-cylinder  then  passes  beneath  the  sarco- 
lemma resting  upon  the  motorial  end  plate,  when  it  divides  into 
two  or  three  primary  branches,  which  further  subdivide  into  a 


i 


:^ 


^i^^-^/^i^-:' 


^iJ 


CT^ 


1 


-I 


..■•:•.■    ."•£,...• ';^  .^,.   J 


^■i:Sc>^--c>iC-<::sS4^ 


■%\j'^' 


Fio.  27. — Motor  Terminations  in  a  Lizard,  Stained  by  METiivLENE-BLrE. — {Landois 

and  Stirling.) 

a.   Muscular  fibers.     !>.  A  nerve  trunk  wliich  splits  up  into  small  Ijranches,  c,   containing  a  few 

medullated  fibers,  d.     The  medullated  fibers,  </,   end  in  motorial  end  plates,  e. 

number  of  ultimate  flat  twigs  expanding  at  their  ends  into  minute 
bulbs.  The  nerve  termination  is  then  a  distinct  arborization, 
each  branchlet  retaining  its  individuality  and  not  anastomosing, 
the  whole  figure  resting  upon  the  motorial  end  plate,  which  in 
turn  is  continuous  with  the  sarcous  element  of  the  muscle-fiber. 
It  is  probable  that  the  contractile  wave  of  the  muscle  has  its 
point  of  origin  in  the  motorial  end  plate. 

The  motor  nerves  for  the  non-striated  or  involuntary  muscles 
are  non-medullated,  and  come  mosdy  from  the  sympathetic 
system.  Near  their  termini  they  ramify  and  form  close  net- 
works or  plexuses  of  fibers.     In  the  angles  formed  by  the  cross- 


THE   HISTOLOGIC   ELEMENTS   OF    THE   NERVOUS   SYSTEM.  47 

ing  of  the  fine  fibrils  composing-  these  plexuses  ganglion  cells 
are  found.  From  these  ganglionic  plexuses  fibrillae  arise  which 
pass  between  the  muscle-fibers  and  continue  parallel  with  them. 
They  frequently  bifurcate  in  their  course,  each  division  giving 
off  small  branches  which  terminate  in  varicose  or  bulbous  ex- 
tremities opposite  the  nuclei  of  the  muscle-cells,  without  passing 
into  them.  According  to  Arnold  and  others,  however,  these 
terminal  fibrillae  pass  into  the  muscle-cells  and  end  in  their 
nuclei. 

NEURONE  OR  NEURODENDRON. 

The  nervous  system  is  known  to  consist  of  a  great  number  of 
anatomic  units  variously  arranged,  which,  after  the  development 
of  their  protoplasmic  processes,  remain  absolutely  independent 
bodies.  These  anatomic  units  have  been  designated  neurones, 
or  nerve  units,  by  Waldeyer,  and  neurodendrons,  or  nerve  trees, 
by  Koelliker.  They  are  the  essential  elements  of  nervous  tissue 
and  possess  peculiar  physiologic,  chemic,  psychic,  and  trophic 
properties. 

The  neurone,  or  nerve  unit,  is  made  up  of  three  parts  :  the 
nerve-cell  body,  the  protoplasmic  processes  of  Deiter,  or,  as  they 
are  now  called  after  His  dendrites,  with  their  terminal  ramifica- 
tions, and  lastly,  the  so-called  axis-cylinder  process,  axone,  or 
neuraxone,  with  its  collateral  branches  and  terminal  end  brushes 
(telodendrons). 

The  neurones  are  arrangred  in  certain  localities  in  distinct 
groups — viz.,  in  the  cortex  of  the  brain  and  cerebellum  they  exist 
in  several  thin  layers  ;  in  the  medulla  oblongata  or  bulb  and 
spinal  cord  they  occur  in  vertical  columns  ;  in  the  central  ganglia 
they  are  arranged  in  distinct  masses.  In  many  locations  they 
occur  singly  or  in  slight  groups. 

The  neurone,  then,  is  a  unit,  an  individual  entity,  consisting  of 
cell-body,  dendritic  processes,  neuraxone,  collaterals,  and  term- 
inal arborizations. 

The  cell-bodies,  or  neurocytes,  present  a  variety  of  forms,  the 
most  generally  distributed  one  being  the  irregular,  large  or  small 
multipolar  form.  The  form  of  cells  have  been  sufficiendy  dis- 
cussed, page  25. 


48  CENTRAL  NERVOUS  SYSTEM. 

The  dendrites,  or  the  protoplasmic  processes  which  arise  trom 
the  irregularities  of  the  surface  of  the  cell-body,  branch  in  various 
directions,  dividing  and  subdividing  like  the  branches  of  a  tree, 
not  anastomosing  with  one  another  or  with  adjacent  or  distant 
dendritic  processes  of  other  cells.  They  are  variable  in  length, 
some  branches  being  quite  long,  whereas  others  are  very  short. 
Their  thickness  also  varies,  some  of  the  short  branches  being 
rather  thick,  while  the  longer  branches  are  quite  thin.  They 
frequently  present  along  their  course  varicose-like  swellings.''' 

They  are  variable  as  to  number,  some  cells  possessing  but  one 
or  two  dendrites,  while  others  possess  from  five  to  seven.  If  the 
finer  dendritic  processes  be  observed  with  a  moderately  high 
power  of  the  microscope,  say  with  a  i  or  i  of  an  inch  objective, 
there  will  be  seen  numerous  minute  protoplasmic  buds  jutting 
from  their  sides.  They  are  somewhat  club-shaped  and  are  very 
minute  in  diameter,  close  to  the  parent  stem,  but  become  longer 
and  larger  to  end  in  bead-like  extremities.  These  lateral  buds 
have  been  termed  gemmules.  They  are  very  abundant  on  the 
dendritic  branches  of  the  cortical  cells  of  the  cerebrum  or  of  the 
Purkinje  cells  of  the  cerebellar  cortex.  Owing  to  the  fact  that 
these  lateral  buds  have  until  very  recently  been  observed  only 
in  specimens  stained  after  the  method  of  Golgi,  they  have  been 
considered  by  some  authors  as  artifacts,  but  Ramon  y'Cajal  has 
shown  that  they  may  be  beautifully  demonstrated  in  specimens 
stained  by  the  intravital  method  of  Ehrlich. 

The  function  of  the  dendrites  is  not  positively  known,  and 
much  of  our  knowledge  is  as  yet  hypothetical.  They  probably 
convey  nerve  impulses  to  the  cell-body  from  which  they  spring, 
influencinor  nerve  terminations  or  filaments  and  other  dendrites 
by  contiguity  of  surface  or  possibly  by  contact  through  the 
gemmules.  From  the  extent  of  surface  occupied  by  the  den- 
drites and  their  ramifications  one  would  believe  that  they  may 
serve  a  nutritional  function,  aidincr  the  nutrition  of  the  cells  of 
which  they  are  a  part. 

The  belief  of  Golgi  that  they  were  connected  with  the  blood- 

*  These  tuber-like  or  varicose  swellings  that  are  seen  on  the  dendrites  of  specimens  pre- 
pared after  the  m;thod  of  Golgi  are  due  to  local  collections  of  chromophyllic  granules  (Len- 
hossek). 


THE    HISTOLOGIC    ELEMENTS    OF    THE    NERVOUS    SYSTEM,  49 

vessels,  and  that  the  nutritive  plasma  was  carried  by  them  to 
the  cell-body  has  been  disproven  by  various  observers. 

Lenhossek  states  that  after  carefully  examining  many  Golgi 
sections  he  failed  to  find  any  connection  between  the  dendrites 
and  the  blood-vessels.  He  further  showed  that  they  were  devel- 
oped long  before  the  blood-vessels.  He  believes  that  they 
absorb  nutritive  plasma  from  all  parts  of  their  surface,  the  plasma 
coming  from  the  lymph-spaces  which  surround  the  dendrites, 
which  spaces  exist  in  great  abundance  throughout  the  central 
nervous  system.  There  is  probably  a  much  greater  circulation 
and  absorption  of  nutritive  plasma  in  the  gray  than  in  the  white 
matter,  because  of  the  abundant  blood  supply  from  the  enormous 
number  of  capillaries  and  the  liberal  lymphatic  distribution  about 
the  blood-vessels,  nerve-cells,  and  processes  in  the  former. 
Berkley  states  that  in  the  cerebral  cortex  the  dendrites  are 
surrounded  by  a  mass  of  nerve-fibers  which  give  off  at  frequent 
intervals  collaterals  which  divide  and  subdivide,  ending  in  little 
bulbs,  which  constitute  the  intracortical  end  apparatus  of  these 
nerve-fibers.  These  little  bulbar  endings  come  into  close  ap- 
proximation with  the  globular  endings  of  the  gemmuies,  and 
he  states  that  it  is  exceedingly  probable  that  the  nervous  im- 
pulses pass  from  cell  to  cell,  or  those  impulses  arising  from  the 
periphery  and  passing  brainward,  pass  across  from  the  bulbous 
endings  of  the  nerve-fibers  to  the  gemmuies  and  through  the 
dendrites  to  the  cell-bodies,  thus  exciting  the  cells  into  activity. 
Berkley  also  states  that  in  many  diseased  conditions — "intoxi- 
cations " — these  lateral  buds  are  the  first  part  of  the  neurone  to 
become  affected  ;  and  he  believes  that  the  early  symptoms  of 
dementia  paralytica  may  be  explained  by  their  destruction  and 
consequent  loss  of  function  as  conductors  of  nervous  impulses. 


THE  NEURAXONE  OR  AXONE. 

The  most  important  of  the  protoplasmic  processes  is  the  one 
which  In  most  cases  is  destined  to  become,  after  receiving  a 
covering  of  myelin,  a  medullated  nerve-fiber.  This  process 
is  the  so-called  axis-cylinder  process,  neuraxone,  or  simply 
axone.  The  neuraxones  are  smooth  throughout,  and  are  usu- 
4 


50  CENTRAL  NlikVOUS  SVSIKM. 

ally  variable  as  to  the  lenL^th  of  their  course,  some  having 
a  short  course,  while  the  course  of  others  is  very  long.  They 
are  of  extreme  fineness,  and  give  off,  at  varying  distances,  side 
branches  called  collaterals  (paraxonen).  These  collaterals  may 
be  seen  issuing  nearly  at  right  angles  from  many  of  the  nerve- 
fibers  composing  the  columns  of  the  spinal  cord  or  the  medulla. 
The  collaterals  frequently  branch,  and  these  in  turn  give  off  deli- 
cate branches,  all  of  which  end  in  fine  brushes  of  fibers  or  arbori- 
zations about  the  dendrites  of  nerve-cells.  The  collaterals  are 
usually  finer  than  the  neuraxones  from  which  they  issue,  and 
often  become  medullated.  The  nerve-fibers,  which  are  simply 
medullated  axis-cylinders,  frequently  divide  toward  the  end  of 
their  course  into  two  or  three  branches,  each  one  retaining  its 
individuality. 

Both  the  axis-cylinder  process,  or  axone,  and  its  collaterals 
(paraxonen)  terminate  or  end  about  nerve-cells  in  brush-like 
expansions  or  tree-like  arborizations,  each  little  branchlet  either 
ending  free  or  in  a  minute  bulbous  expansion.  These  terminals 
are  termed  the  telodendrons.  As  a  rule,  to  which  there  are 
but  few  exceptions,  the  neurones  throughout  the  cerebrospinal 
system  possess  but  one  neuraxone,  the  exceptions  being  found 
in  the  cells  of  the  posterior  spinal  ganglia,  which  often  possess 
two  axones,  one  passing  centrally,  dividing  T-shaped  in  the 
spinal  cord,  one  division  passing  vertically  upward,  the  other 
downward,  each  giving  ofi^  at  right  angles  numerous  collaterals 
which  enter  the  gray  matter  of  the  cord.  The  other,  a  periph- 
eral axone,  passes  peripherally  to  terminate  in  a  sensory  end 
organ.  The  cells  of  the  ganglia  connected  with  the  sensory 
cranial  nerves  have  somewhat  similar  connections,  possessing 
two  axones,  one  central  and  one  peripheral. 

The  Cajal  cells  in  the  outer  or  molecular  layer  of  the  cerebral 
cortex  are  known  to  possess  two  or  more  axones.  They  form 
a  distinct  type  of  neurone  (Fig.  29). 

Some  of  the  cells  of  the  visceral  sympathetic  ganglia  have 
many  axones  or  axis-cylinder  processes. 

Neurones  may  be  classified  into  three  chief  types:  (i)  Those 
whose  axones  are  very  long,  giving  off  collaterals,  but  retaining 
their   individuality.     They  pass   directly  into    the  white   matter 


THE    HISTOLOGIC   ELEMENTS   OF    THE   NERVOUS   SYSTEM.  51 

and  become  medullated  nerve-fibers,  ending  in  near  or  distant 
parts  of  the  nervous  system,  or  in  periplieral  end  organs. 
Because  the  cells  of  the  anterior  horns  of  the  spinal  cord, 
whose  functions  are  known  to  be  motor,  all  possess  so  long  a 
neuraxone  Golgi  termed  this  first  type  of  neurone  "  motor." 
We  know  positively,  however,  that  long  axones  are  possessed 
not  only  by  motor  neurones,  but  by  sensory  ones  as  well — as, 
for  example,  the   neurones  of  the  multipolar  cells  of  the  ves- 


FiG.  28. — A  Large  Cell  of  the  Second  Type  of  Golgi  from  the  Granular  Layer 
OF  THE  Cerebellum. — {After  KoelUker.) 

icular  column  of  Clarke,  which  pass  across  through  the  white 
matter  of  the  cord  and  become  vertical  in  the  direct  cerebellar 
tract,  thence  passing  upward  to  terminate  in  the  cerebellum. 
Another  example  of  long  axones  may  be  mentioned,  the 
ascending  branches  of  the  posterior  nerve-roots,  many  of  which 
continue  throughout  the  whole  length  of  the  posterior  columns 
and  terminate  in  the  medulla  about  the  cells  of  the  nuclei  of  the 
posterior  columns. 


52 


CENTRAL   NKRVOrS  SYSTEM. 


'xS 


In  the  neurones  of  tlie  second  type,  or 
second  type  of  Golgi,  the  neuraxones,  after  a 
short  course,  break  up  into  innumerable  fine 
tilaments  which  form  netvvorlvs,  thus  losing- 
their  individuality.  Because  of  their  abund- 
ance in  the  gray  matter  adjacent  to  the  pos- 
terior horns,  which  is  presumably  sensory  in 
function,  Golgi  concluded  that  this  type  of 
neurones  was  also  sensory  in  character.  It 
may  be  stated  here  that  the  axones  of  this 
second  type  of  neurone  rarely,  if  ever,  leave 
the  gray  matter,  and  their  function  is  that 
of  association.  Cajal  denies  their  sensory 
character  and  states  that  cells  with  short 
axones  are  distributed  throughout  the  cen- 
tral nervous  system  (Fig.  28). 

The  third  type  of  neurones  are  those 
which  have  been  recendy  described  by 
Ramon  y'  Cajal,  and  hence  are  often  called 
the  Cajal  cells.  They  have  only  been  found 
in  the  molecular  or  outer  layer  of  the  cortex. 
They  consist  of  small  cells,  which  are  varia- 
ble as  to  shape,  the  spindle  shape  being  the 
type.  The  axones  from  these  cells  have  a 
horizontal  course  and  are  constantly  giving 
off  ascending  collaterals  which  terminate  in 
the  outermost  part  of  the  molecular  layer  in 
minute  bulbous  expansions  (Fig.  29). 

Neurones  are  also  divided  according  to 
their  functions  into  three  general  classes : 
motor,  sensory,  and  associative. 


Fic.  29. — Three  Cajai. 
Cells  from  the  Cor- 
tex  OF    THE   Gyrus 

FORNICATUS        OK        A 

Doa.—{A//er     Koelli- 
ker.) 


THE   NEUROGLIA. 

This  is  the  name  applied  to  the  tissue 
which  forms  the  supporting  framework  of 
the  central  nervous  system.  So  closely  does 
it  resemble  connective   tissue  in  appearance 


/■'ig  2 


Fi^3 

Fig.  30. — Motor  and  Sensory  Neurones. — [Jacobus  Atlas.) 

Fig.  I. — A  large  motor  or  pyramidal  cell  from  the  cortex  of  the  cerebrum,  with  its  apical  tree- 
like branching  protoplasmic  processes  or  dendrites  possessing  numerous  lateral  buds  or  gem- 
mules.  This  cell  possesses  a  single  long  slender  basal  process,  ax,  or  axone  (axis-cylinder 
process),  which  gives  off  at  right  angles  collateral  branches,  b.  This  cell  with  its  processes 
forms  a  central  motor  neurone. 

Fig.  2. — Represents  a  single  motor  or  ganglionic  cell  from  an  anterior  horn  of  the  spinal  cord, 
with  its  numerous  dendrites  and  a  single  axone,  ax,  which  axone  terminates  in  a  motor  end 
plate,  the  whole  forming  a  peripheral  motor  neurone. 

Fig.  3. — Indicates  schematically  the  relationship  between  the  cortical  and  peripheral  motor  neu- 
rones and  between  the  peripheral  and  central  sensory  neurones. 

53 


THE    HISTOLOGIC   ELEMENTS   OF    THE    NERVOUS    SYSTEM. 


55 


and  function  that,  until  within  a  recent  period,  it  was  con- 
sidered by  most  anatomists  identical  to  that  tissue.  Virchow, 
however,  as  far  back  as  1846,  discovered  its  true  nature 
from  the  histologic  study  of  sections  of  the  brain  beneath  the 
ependyma  of  the  ventricles.  He  discovered  a  structureless 
membrane  which  he  believed  differed  from  true  nerve-cells  and 
fibers  and  was  perfectly  satisfied  that  this  tissue,  which  in  1853 


Fig.  31. — MicROPHOTOGRAPH  OF  Neuroglia  Cells.     Showing  the  relation  they  bear  to  the 
capillary  blood-vessels.     Stained  after  the  Cox-Golgi  method. 

he  named  neuroglia,  differed  decidedly  from  connective  tissue. 
He  also  observed  that  neuroglia  tissue  did  not  occur  in  the 
peripheral  nerves,  and  that  the  blood-vessels  of  the  nervous 
system  were  surrounded  by  it.  Owing  to  the  embryologic 
researches  of  His  and  the  histologic  studies  of  Golgi,  Ramon  y'- 
Cajal,  Beneke,  Weigert,  and  Mallory,  and  the  publication  by 
the  last  two  authors  of  their  selective  methods  of  staining,  we 
are  enabled  to  understand  more  accurately  than  ever  before  the 


56  CENTRAL   NKKVOL'S  SYSTEM. 

origin  and  histologic  structure  of  neuroglia  tissue.  This  tissue, 
which  is  epiblastic  in  origin,  is  composed  of  cells  and  their 
processes,  which  cells  bear  the  various  names  of  spider  cells  of 
Deiter,  sflia  cells,  neuroglia  cells,  and  stellate  cells  or  astrocytes. 
They  are  of  two  chief  forms — large  and  small  spheric.  The 
cell-body  is  somewhat  irregular  in  outline,  is  composed  of  pro- 
toplasm and  contains  a  nucleus  large  in  size  and  spheric  in 
shape.  These  cells  vary  from  six  to  thirteen  v-  in  diameter. 
The  large  spheric  cells  contain  granular  chromatin,  while  the 
chromatin  in  the  small  spheric  cells  appears  as  a  dark  homo- 
geneous mass.  Hy  another  classification  the  cells  are  divided 
according  as  their  processes  are  long  or  short.  In  the  former — 
z.  <?.,  those  having  long  processes^ — delicate  filaments  are  given 
off  in  a  radiating  manner  from  all  parts  of  the  cell-body  ;  these 
processes  are  very  fine,  of  uniform  thickness,  and  occasionally- 
bifurcate  near  their  extremities,  usually,  however,  remain- 
ing entire  to  their  ends.  They  do  not  anastomose  with  each 
other,  have  no  varicosities,  and  are  solid  and  smooth  throughout. 
A  few  of  these  cells  have  brush-like  processes  springing  from 
one  or  both  ends.  The  neuroglia  cells  with  long  processes 
exist  mostly  in  the  white  matter. 

In  the  cells  of  the  second  form,  those  with  short  processes, 
the  filaments  are  not  so  long,  are  more  irregular,  and  somewhat 
thicker  than  are  those  of  the  first  form.  These  cells  are  found 
with  but  few  exceptions  in  the  gray  matter,  and  resemble  very 
closely  some  of  the  small  forms  of  multipolar  nerve-cells,  from 
which  they  are  with  difficulty  differentiated.  The  fibers  vary  in 
size  from  those  of  extreme  fineness  to  those  of  fifteen  //  in 
thickness.  The  latter  fibers  are  only  found  where  pathologic 
changes  produce  complete  or  incomplete  destruction  of  nervous 
tissue,  when  they  are  in  reality  hypertrophied. 

It  is  a  remarkable  fact  that  when  degeneration  changes  occur 
in  the  central  nervous  system,  the  place  of  the  destroyed  tissue 
becomes  in  large  part  occupied  by  an  increase  of  neuroglia 
tissue.  It  should  be  remembered  that  while  neurooflia  tissue 
resembles  very  closely  connective  tissue  in  function,  it  differs 
decidedly  from  it  in  development,  the  former  being  epiblastic 
while  the  latter  is  mesoblastic  in  oricrin. 


THE   HISTOLOGIC   ELEMENTS   OF   THE   NERVOUS   SYSTEM. 


57 


In  discussing  the  question  as  to  the  relation  of  the  processes 
to  the  neurogha  cells,  Weigert  states  that  while  in  embryonic 
life  they  are  parts  of  the  cell,  later  the  processes  are  lost  to  the 
cell-bodies,  and  the  latter  exist  free  in  the  network  of  neuroglia 
fibers.  He  bases  his  conclusions  on  the  facts  that  the  fibers 
are  no  longer  of  the  same  chemic  composition  as  the  proto- 
plasm of  the  cell-bodies,  and  that  the  fibers  react  to  his  recent 
differential  stain  unlike  protoplasm.     He  also  believes  that  the 


Fig.  32. — Three   Neuroglia   Cells   (Astrocytes).     Showing   the  relation  the  neuroglia 
processes  bear  to  the  cell-body. — [After  Weigert. ) 


neuroglia  cells  and  fibers,  while  epiblastic  in  development, 
differ  decidedly  from  the  true  nervous  tissue,  his  reasons  being 
that  neuroglia  tissue  proliferates  when  the  nervous  system 
becomes  diseased,  and  that  with  his  new  neuroglia  stain,  true 
nervous  tissue  remains  unstained,  while  neuroglia  tissue  stains 
blue.  In  gliomatous  tumors,  which  are  made  up  almost  entirely 
of  neuroglia  fibers  and  cells,  it  is  quite  common  to  find  in  cer- 
tain parts  of  the  growth  neuroglia  cells  with  processes  lying  in 


CKN TRAI.   NKRVOL'S  SYSTEM. 


a  meshwork  ot  differentiated  fibers,  while  in  other  locaHties 
neurogha  cells,  with  [)rocesses  radiating  from  all  surfaces  of  the 
cell-body,  or  else  coming  from  either  pole,  may  be  observed. 


BLOOD-VESSELS  AND   LYMPHATICS. 

The  blood-vessels  of  the  central  nervous  system  differ  some- 
what from  those  in  the  other  parts  of  the  body ;  it  will  therefore 
be  necessary  to  give  a  brief  description  of  them  here. 

The  arteries  of  the  brain  and  cord,  like  similar  vessels  else- 
where in  the  body,  possess  three  distinct  coats,  but  tlie  inner 
coat  is  subdivided  so  that  the  larger  arteries  may  be  said  to 
possess  four  coats — viz.,  an  outer  coat,  or  tunica  adventitia ;  a 
middle  or  muscular  coat,  the  tunica  media  ;  and  an  inner  coat, 
the  tunica  intima,  which  is  further  subdivided  into  two  layers, 
an  outer  or  elastic  lamina,  the  membrana  fenestra,  and  an  inner 
or  endothelial  layer. 

The  Tunica  Adventitia. — The  tunica  adventitia  of  the 
larger  arteries  is  composed  of  connective  tissue  continuous  with 
the  pia  mater.  In  the  smaller  arteries  this  adventitial  coat  con- 
sists of  a  delicate  membranous  investment,  lightly  striated, 
containing  connective-tissue  cells,  stellate  or  fusiform  in  shape, 
and  possessing  round  or  oval-shaped  nuclei.  This  coat  is  fre- 
quently pigmented  and  often  contains  fat  granules.  While  this 
outer  coat  is  loosely  applied  to  the  middle  coat,  or  tunica  media, 
there  exists  between  them  a  distinct  space  filled  with  lymph, 
w^hich  presents  ampullar  dilatations  in  the  angles  formed  by 
the  branching  of  vessels.  This  space  is  termed  the  adventitial 
lymph-space,  or  Virchow-Robin  space.  If  sections  of  hardened 
brain-tissue  are  examined  microscopically,  distinct  spaces  will 
be  found  outside  of  the  adventitial  coat,  which  are  so  much 
larger  than  the  diameter  of  the  vessels  that  they  form  distinct 
channels  in  which  the  vessels  rest ;  these  are  the  perivascular 
lymph  canals  or  spaces  of  His.  They  possess  no  endothelial 
lining.  These  channels  communicate  with  the  epicerebral  space 
located  between  the  outer  surface  of  the  cortex  and  the  pia 
mater. 

All  the  vessels  of  the  central  nervous  system  have  a  strong 


TFIE    HISTOLOGIC    ELEMENTS   OF   THE    NERVOUS    SYSTEM. 


59 


protective  coat  of  neuroglia  tissue,  which  may  have  the  func- 
tion of  preventing  injury  to  the  brain  tissue  from  too  great  arte- 
rial pressure. 

Tunica  Media. — The  tunica  media  consists  of  smooth,  non- 
striated  muscle-fibers  arranged  transversely  to  the  long  axis  of 
the  vessel,  thus  placing  the  spindle  muscle-cells  at  right  angles 
to  the  vessel  wall,  the  muscle  nuclei  and  those  of  the  endothe- 


FiG.  33. — Neuroglia  Cells  from  the  Cerebral  Cortex  of  a  Dog's  Brain.     Showing 
their  connection  with  blood-vessels. — {After  Koelliker.') 


Hum  of  the  inner  coat  appearing  to  cross  one  another.  In  the 
small  cerebral  vessels  this  tunic  differs  from  vessels  of  a  corre- 
sponding size  among  the  systemic  arteries  in  that  it  contains 
a  single  layer  of  circularly  arranged  muscle-fibers. 

Tunica  Intima. — The  tunica  intima  consists  of  an  inner  or 
endothelial  layer,  which  is  merely  a  tube  of  squamous  endothe- 
lial cells  united  at  their  margins  by  cementine  and  pos- 
sessing   Oval  nuclei,  which  are  arranged  longitudinally,  having 


6o  CENTRAL  NERVOUS  SYSTEM. 

their  longest  diameter  in  the  direction  of  the  vessel's  lentrth. 
The  outer  or  elastic  layer  is  a  delicate  elastic  membrane  which, 
for  the  smaller  arteries,  has  no  definite  structure.  It  gives  to  the 
larger  arteries  an  appearance  of  longitudinal  striation.  The 
presence  of  this  layer  in  the  smaller  arteries  is  doubted  by  many 
histologists, 

VEINS. 

The  veins  have  three  coats  similar  to  those  of  the  arteries. 
The  tunica  media,  however,  differs  from  that  of  the  arteries  in 
that  it  consists  wholly  of  connective  tissue,  being  devoid  of 
muscle-fibers,  and  is,  in  the  smaller  vessels,  destitute  of  elastic 
fibers.  In  consequence  of  these  changes  in  the  media  the  cali- 
ber of  the  veins  is  larger,  the  vessel  wall  thinner  and  more  lax. 
They  contain  no  valves. 

CAPILLARIES. 

The  capillaries  of  the  cerebrospinal  system  are  exceedingly 
minute,  some  of  them  being  smaller  than  the  average  diameter 
of  a  red  blood-corpuscle.  They  vary  from  four  to  eight  m  in 
diameter  (about  ^^nr  of  an  inch).  It  is  possible  that  various 
hardening  reagents  narrow  the  diameter  of  the  capillaries,  and 
that  in  the  living  state  they  are  not  so  small,  their  lumen  per- 
mitting the  passage  of  the  red  celk.  It  is,  however,  perfectly 
possible  for  the  red  corpuscles,  owing  to  their  elasticity,  to  circu- 
late through  capillaries  whose  diameter  is  less  than  the  diameter 
of  the  corpuscles.  The  capillaries  may  be  distinguished  micro- 
scopically by  the  disappearance  of  the  muscular  coat  and  the 
continuation  of  a  vessel  as  a  simple  tube  consisting  only  of  an 
endothelial  lining  and  having  a  slight  adventitial  sheath.  The 
former  is  a  continuation  of  the  endothelium  of  the  smaller 
arteries,  and  consists  of  elongated  fusiform  cells,  which  stain 
beautifully  with  silver  nitrate,  with  oval  nuclei ;  the  nuclei  are 
well  stained  with  a  saturated  solution  of  methylene-blue.  The 
slight  adventitial  layer  is  the  remains  of  the  tunica  adventitia  of 
the  larger  vessels,  and  its  presence  is  indicated  by  a  few  round 
or  oval  nuclei,  with  a  few  nucleated  connective-tissue  cells  ar- 
ranged in  a  longitudinal  manner  outside  of  the  endothelial  layer. 


THE    HISTOLOGIC   ELEMENTS   OF   THE   NERVOUS   SYSTEM. 


6i 


LYMPHATICS. 

The  lymphatics  of  the  central  nervous  system  are  confined  to 
certain  spaces  about  the  blood-vessels  and  nerve-cells  and  to 
channels  which  appear  as  if  tunneled  out  of  the  nervous  sub- 
stance. True  lymphatic  vessels  or  lymph-glands  have  never 
been  discovered  within  the  cranial  cavity  or  in  the  spinal  canal. 


Fig.  34.— a  Capillary  Blood-vessel  from  the  Gray  Matter  of   the  Spixal   Cord 
OF  AN  Ox.     Stained  with  methylene-blue  and  magnified  400  diameters. 


The  lymph-spaces,  which  are  very  abundant  throughout  the 
nervous  system,  communicate  at  the  surface  of  the  brain  and  cord 
with  the  subarachnoid  space.  This  latter  space  in  the  brain  com- 
municates, according  to  Key  and  Retzius,  with  the  venous  sinuses 
by  means  of  the  Pacchionian  bodies,  which  bodies  may  be  consid- 
ered as  outlets  for  the  subarachnoid  (cerebrospinal)   fluid.      The 


62  CKX  rRAI.  XKRVOUS  SVSTKM. 

spinal  and  cranial  nerves,  as  they  pass  out  through  their  respective 
foramina,  receive  prolongations  in  the  form  of  tubular  sheaths 
from  the  dura,  pia,  and  arachnoid  membranes.  The  spaces 
between  these  sheaths  are  lymphatic  in  nature  and  communicate 
with  the  subdural  and  subarachnoid  spaces.  These  perineural 
spaces  are  considered  by  many  observers  as  outlets  for  the  sub- 


FiG.  35. — A  Camera  Luciija  Drawing  of  a  part  uf  the  Gray  Matter  of  the 
Anterior  Horn.     Showing  pericellular  and  perivascular  lymph  channels. 

arachnoid  fluid.  This  seems  proven  for  the  optic  nerve  and  for 
some  of  the  spinal  nerves.  The  sheaths  that  surround  the 
optic  nerve  remain  distinct  from  one  another,  so  that  the  peri- 
neural spaces  maybe  injected  through  the  subdural  and  sub- 
arachnoid cavities.  William  Browning  has  proven  that  the  peri- 
neural spaces  about  the  lumbar  and  sacral  nerves  may  be 
injected  through   the  subarachnoid  cavity  in  lower  animals  at  all 


THE    HISTOLOGIC    ELEMENTS   OF    THE    NERVOUS    SYSTEM.  63 

ages,  but  in  man  only  during-  fetal  life,  as  the  spaces  become 
obliterated  shortly  after  birth.  Hence  these  spaces  may  be 
considered  as  outlets  for  the  subarachnoid  fluid  in  the  lower 
animals,  but  in  the  human  body  only  during  the  intra-uterine  life. 


THE  ADVENTITIAL  LYMPH-SPACE. 

In  describing  the  histology  of  the  blood-vessels  of  the  nervous 
system  mention  was  made  of  a  space  which  exists  between  the 
tunica  media  and  tunica  adventitia  ;  this  space  is  very  narrow, 
save  in  the  angle  formed  by  the  branching  of  the  vessel  where  it 
presents  ampullar  dilatations.  These  spaces  are  continued 
around  the  smaller  arteries  and  capillaries  throughout  the  central 
nervous  system.  Those  of  the  brain  pass  out  of  the  cranial 
cavity  with  the  carotid  and  vertebral  arteries  and  terminate  in 
the  deep  cervical  glands. 

In  addition  to  the  adventitial  lymph-spaces,  small  channels 
exist  in  which  the  small  blood-vessels  and  capillaries  rest ;  they 
appear  as  if  tunneled  out  of  the  nervous  tissue,  and  are  called 
the  perivascular  lymph-canals  of  His.  They  do  not  possess  a 
lining  membrane ;  the  adventitial  sheath  of  the  blood-vessel, 
however,  is  closely  applied  to  the  walls  of  the  canal.  In  the 
walls  of  these  channels  exists  a  matrix  of  neuroglia,  processes  of 
which  pass  across  each  space  and  become  connected  with  the 
adventitial  sheath  of  the  contained  vessel.  Whether  these  neu- 
roglia processes  aid  in  the  absorption  of  lymph  is  as  yet  unknown. 


PERICELLULAR  LYMPH-SPACES. 

Surrounding  the  nerve-cells  of  the  cerebrospinal  nervous 
system  exist  numerous  oval,  round,  or  polygonal-shaped  spaces, 
which  in  hardened  specimens  at  least  are  much  greater  in 
diameter  than  are  the  nerve-cells  which  rest  within  them.  These 
pericellular  spaces  are  continuous  with  the  adventitial  lymph- 
spaces  into  which  they  drain. 


CHAPTKR    II. 

SPINAL    CORD. 

The  spinal  cord,  or  medulla  spinalis,  is  located  in  the  vertebral 
canal,  and  is  enveloped  by  three  membranes — viz.,  the  outer,  or 
dura  mater  ;  the  middle,  or  arachnoidean  membrane  ;  and  the 
inner,  or  pia  mater.  These  membranes  protect  the  cord  and 
give  support  to  its  nutrient  vessels.  The  dura  (so  called  from 
the  Latin  durus,  hard)  is  a  strong  fibrous  membrane  continuous 
with  the  dura  of  the  brain.  It  surrounds  the  cord  and  the  plexus 
of  nerves  called  the  cauda  equina  in  a  loose,  sac-like  manner, 
and  is  separated  from  the  bony  canal  of  the  vertebrae  by  loose 
areolar  tissue  and  by  a  plexus  of  veins — the  vertebral  plexus. 
This  space  between  the  bone  and  the  dura  is  called  the  epidural 
space.  The  dura  is  attached  above  to  the  circumference  of  the 
foramen  magnum,  and  below  to  the  third  sacral  vertebra,  from 
which  it  extends  as  a  fibrous  cord  to  the  periosteum  of  the 
coccyx.  Double  openings  exist  opposite  the  intervertebral 
foramina  for  the  transmission  of  the  spinal  nerves  ;  processes 
of  this  membrane  surrounding  these  nerves  at  their  exit  forming 
tubular  sheaths.  The  dura  of  the  cord  differs  from  that  of  the 
brain  in  several  respects — /.  e.,  it  does  not  form  the  periosteum 
of  the  vertebral  canal  ;  it  sends  no  processes  into  the  median 
fissures  of  the  cord  ;  nor  does  it  separate  into  lamina  for  the 
formation  of  venous  sinuses.  The  dura  consists  of  dense 
bundles  of  connective  tissue  intermingled  with  elastic  fibers  ;  in 
the  spaces  between  the  fibers  exist  flattened  connective-tissue 
corpuscles.  The  inner  surface  of  the  dura  is  lined  with  endo- 
thelium, and  is  abundantly  supplied  with  nerves  and  blood- 
vessels. The  small  connective-tissue  spaces  serve  for  the 
lymph  supply  to  the  membrane. 

64 


SPINAL  CORD.  65 

The  spinal  arachnoid,  from  the  Greek  o-pdy-^ri^  spider's  web,  is  a 
loose,  delicate  membrane,  seen  on  removing  the  dura.  It  is 
connected  with  the  membrane  beneath,  the  pia,  by  many  delicate 
connective-tissue  bands  lined  with  endothelium,  and  separated 
by  a  congeries  of  spaces  differing  in  size.  These  spaces  are 
filled  with  cerebrospinal  fluid,  and  together  receive  the  name  of 
the  subarachnoid  space.  The  arachnoid  is  devoid  of  nerves 
and  has  a  very  slight  blood  supply.  It  consists  of  very  deli- 
cate connective-tissue  fibers,  which  interlace  with  one  another 
and  are  lined  with  delicate  pavement  epithelium. 

It  is  rather  loosely  attached  to  the  under  surface  of  the  dura 
mater,  there  existing  between  the  two  membranes  a  space 
called  the  subdural  space,  though  in  some  situations  the  attach- 
ment is  so  close  that  no  such  space  exists. 

A  space  above  referred  to  of  much  greater  size  exists  beneath 
this  membrane,  between  it  and  the  pia  mater,  called  the  sub- 
arachnoid space.  This  space  is  divided  on  each  side  by  a  fibrous 
septum,  the  ligamentum  denticulatum,  into  an  anterior  and  a 
posterior  subarachnoid  space,  continuous  with  the  corresponding 
subarachnoid  spaces  of  the  brain  and  communicating  with  the 
general  ventricular  cavities  of  the  brain  by  means  of  several 
small  openings  in  the  pia  mater  of  the  medulla  oblongata. 
These  subarachnoidal  spaces  contain  an  abundant  serous  secre- 
tion, the  cerebrospinal  fluid,  and  may  be  regarded  as  lymphatic 
reservoirs. 

The  pia  mater  (from  the  Latin  pia,  tender,  mater,  mother) 
closely  invests  the  cord,  forming  its  connective-tissue  sheath  or 
neurilemma.  So  closely  adherent  is  it  to  the  cord  that  it 
can  not  ordinarily  be  removed  without  lacerating  the  cord.  It 
gives  off  tubular  prolongations  upon  the  spinal  nerves.  The 
pia  at  the  lower  end  of  the  cord  becomes  contracted,  and  enters 
into  the  formation  of  the  filum  terminale  and  blends  with  the 
dura  mater  at  the  third  sacral  vertebra.  The  pia  consists  of  an 
outer  and  an  inner  layer,  the  outer  layer  supporting  the  blood- 
vessels, the  inner  layer  being  much  less  vascular  and  composed 
of  circularly  arranged  connective-tissue  fibers.  The  ventral 
septum,  a  process  of  pia  mater,  passes  into  the  anterior  median 
fissure  conveying  blood-vessels  to  the  cord. 
5 


66 


CENTRAL   NERVOUS   SYSTEM. 


W: 


^! 


f#"i 


Si 


The  ligamentum  denticulatum,  or  dentate 
lioament,  is  a  fibrous  band  located  on  each 
side  of  the  spinal  cord  and  separating  the 
anterior  from  the  posterior  roots  of  the 
spinal  nerves.  It  also  serves  to  separate 
the  general  subarachnoid  cavity  into  two 
compartments,  anterior  and  posterior.  It 
is  composed  of  triangular  dentations, 
twenty  or  more  in  number,  whose  inner 
broader  portions  are  connected  with  the 
pia,  the  outer  being  connected  with  dura 
mater  (Fig.  2)l)  I  below  it  becomes  con- 
tinuous with  the  filum  terminale.  Its  func- 
tion is  to  support  the  cord  in  the  fluid  in 
which  it  lies. 

The  spinal  cord,  located  in  the  vertebral 
canal  and  surrounded  by  its  membranes, 
extends  from  the  upper  border  of  the  atlas 
to  the  body  of  the  first  or  second  lumbar 
vertebra.  It  varies  in  length  from  sixteen 
to  eighteen  inches,  about  forty-five  centi- 
meters. Its  weight  is  about  fifty  grams — 
I  yi  ounces.     Above,  it  is  continuous  with 


Fig.  36. — View  from  Behind  of  the  Lower  End  of 
THE  Spinal  Cord  with  the  C.vuda  Equina  and 
DuRAL  Sheath. — {Alien  T/iomson.) 

The  sheath  has  been  opened  from  behind  and  stretched  toward 

the  sid^s ;  on  the  left  side  all  the  roots  of  the  nerves  are 

entire  ;  on  the  right  side  both  roots  of  the  first  and  second 

lumbar  nerves  are  entire,  while  the  rest  have  been  divided 

close  to  the  place  of  their  passage  through  the  sheath.     The 

bones  of  the  coccyx  are  sketched  in  their  natural  relative 

position  to  show  the  place  of  the  filum  terminale  and  the 
Fig.  36.  ;         .  ^ 

■-'  lowest  nerves. 

a.   Placed  on  the  posterior  median  fissure  at  the  middle  of  the 

lumbar  enlargement  of  the  cord,      b,  b.   The  terminal  filament,  drawn  slightly  aside  by  a 

hook  at  its  middle,  and  descending  within  the  dural  sheath,     b' ,  b' .   Its  prolongation  beyond 

the  sheath  and  upon  the  back  of  the  coccygeal  bones,     c.   The  dural  sheath,     d.   Double 

foramina  in  this  for  the  separate  passage  for  the  ventral  and  dorsal  (anterior  and  posterior) 

roots  of  each  of  the  nerves,     e.  Ligamentum  denticulatum.     Dx  and  Dxii.   The  tenth  and 

twelfth  thoracic  (dorsal)  nerves.     Li  and  Lv.  The  first  and  fifth  lumbar  nerves.     Si  and 

Sv.   The  first  and  fifth  sacral  nerves.     Ci.  The  coccygeal  nerve. 


% 


Svj 


^Ci 


Fig.  37. — Photograph  of  Human  Spinal  Cord. 

A.  Dura  mater.      B.   Anterior  spinal  artery.      C.   AracTinoid.     D.   Ligamentum  denticulatum. 

E.   Filum  terminale.      F.   Cauda  equina. 

67 


SPINAL  CORD.  69 

the  medulla  oblongata,  or  bulb,  which  is  an  enlarged  upward  ex- 
tension of  it,  and  below  it  terminates  in  a  very  slender  process, 
the  filum  terminale  or  central  ligrament  of  the  cord.  The  filum 
terminale  at  its  upper  part  contains  a  few  spheric  cells  which  lie 
near  the  central  canal.  These  pale  nucleated  cells  are  from  1 1 
to  13  «  in  diameter.  In  addition,  one  may  observe  the  processes 
from  the  cells  which  encircle  the  central  canal,  the  so-called 
ependymal  cells.  Surrounding  the  filum  terminale  is  a  leash 
of  nerves  made  up  of  the  descending  lumbar  and  sacral  nerves, 
called,  from  its  resemblance  to  a  horse's  tail,  the  cauda  equina. 

An  enlarged  central  canal  extends  through  about  half  of  the 
extent  of  the  filum  terminale ;  below,  the  latter  terminates  in  a 
slender  thread-like  process  of  pia  mater  containing  the  end  of  the 
anterior  spinal  artery  and  vein  ;  this  process  perforates  the  dura 
mater,  which  lends  to  it  a  sheath  and  becomes  blended  with  the 
periosteum  of  the  sacral  canal  or  the  back  of  the  coccyx. 

The  spinal  cord  is  cylindric,  somewhat  flattened  on  its  anterior 
and  posterior  surfaces,  rounded  from  side  to  side.  It  presents 
two  enlargements  :  the  cervical  or  brachial  enlargement,  the 
larger  one,  extending  from  the  third  cervical  to  the  first  or  second 
dorsal  vertebra,  and  the  lumbar  enlargement,  extending  from  the 
spinous  processes  of  the  ninth  or  tenth  dorsal  to  the  first  lumbar 
vertebra.  That  portion  of  the  cord  between  the  two  enlarge- 
ments is  known  as  the  dorsal  cord ;  it  gives  origin  to  the  inter- 
costal nerves.  These  enlargements  of  the  cord  are  due  to  the 
fact  that  at  these  points  the  nerves  of  the  extremities — in  the 
cervical  region  those  of  the  upper  limbs,  in  the  lumbar  region 
those  of  the  lower  limbs — unite  with  the  cord.  Below  the  lumbar 
enlargement  the  cord  tapers  in  the  form  of  a  cone, — the  conus 
medullaris, — the  apex  of  which  gives  off  the  slender  filament,  the 
filum  terminale.  The  embryonic  cord  completely  fills  the  verte- 
bral canal,  but  after  the  third  month,  because  of  the  more  rapid 
growth  of  the  vertebral  canal  and  of  the  sacral  and  lumbar 
nerves,  the  cord  appears  to  recede  from  below,  reaching  only 
to  the  first  or  second  lumbar  vertebra.  The  cord  may  be 
considered  as  being  made  up  of  a  number  of  segments  super- 
imposed one  upon  the  other,  each  segment  corresponding  to  the 
entrance  and  exit  of  a  pair  of  spinal  nerves.     Thus,  we  speak  of 


70 


CENTRAL  NERVOUS  SYSTEM. 


cervical,  dorsal,  lumbar,  or  sacral  segments.  The  different 
seonients  of  which  the  cord  consists  are  continuous  with  one 
another,  there  being"  no  lines  of  division  or  constrictions  to 
indicate  their  separation.'''    The  nerve-roots  leave  the  segments 


Fig.  38. — Diagram  showing  the  Relative  Size  and   Form   of   Different  Segments 
OF  the  Coccygeal,  Sacral,  Lumbar,  Dorsal,  and  Cervical  Cord. — {After  Gowers.) 

in  a  horizontal'  direction  ;  they  consist  of  an  anterior  pair,  which 
are  motor  in  function,  and  of  a  posterior  pair,  which  are  sensory. 
On  the  posterior  nerve-roots  of  both  sides  may  be  observ^ed  a 


*  The  transition  of  the  spinal  cord  into  the  medulla  is  a  very  gradual  one,  there  being  no 
sharp  line  of  demarcation.  The  anatomic  division  line  which  is  usually  accepted  is  the  exit  of 
the  first  cervical  nerve,  which  passes  out  between  the  occipital  bone  and  atlas. 


SPINAL  CORD. 


71 


small  oval  ganglion — the  posterior  spinal  ganglion.  Although 
the  nerve-roots  emerge  from  the  cord  in  a  horizontal  direction, 
they  soon  become  oblique,  and  gradually  almost  vertical,  in  their 
direction. 

The  cord,  on  tran verse  section,  is  nearly  circular,  slightly  flat- 
tened from  before  backward,  and  varies  in  size  and  shape 
according  to  the  region  from  which  the  section  is  made.  It  is 
largest  in  the  cervical  and  lumbar  regions  and  smallest  in  the 
dorsal  and  sacral  regions.     It  consists  of  two  distinct  parts  :  an 


Fig.  39. — A,  Transverse  Section  of  the  Human  Spinal  Cord  through  the  Mid- 
lumbar  Region  to  Show  Its  General  Topography.     Weigert's  stain. 


inner  part,  or  gray  matter,  shaped  somewhat  like  the  letter  H, 
consisting  of  symmetric  halves  united  by  two  bands  of  nervous 
matter,  the  commissures;  and  an  outer  part  of 'white  matter, 
which  almost  completely  surrounds  the  gray.  The  white  matter 
is  incompletely  divided  into  halves  by  an  anterior  longitudinal, 
or  ventral,  and  a  posterior  longitudinal,  or  dorsal,  fissure.  The 
ventral  one  is  shorter  and  much  broader  than  the  dorsal,  and 
has  extending  centrally  into  it  a  process  of  pia  mater,  the  ventral 
septum,  which  conducts  blood-vessels  to  the  cord.     This  anterior 


72  CENTRAL  NERVOUS  SYSTEM. 

fissure  extends  backward,  and  has  for  its  posterior  boundary  the 
anterior  or  white  commissure.  Tlie  posterior  or  dorsal  fissure 
is  a  mere  landmark,  there  being  no  actual  fissure  present,  this 
landmark  being  occupied  not  by  a  process  of  pia  mater,  but  by 
a  process  of  neuroglia  tissue  carrying  wath  it  blood-vessels. 
Each  half  of  the  cord  is  further  subdivided  by  a  posterolateral 
groove,  made  by  the  entrance  of  the  posterior  nerve-roots,  and 
by  an  anterolateral  slit,  due  to  the  outward  passage  of  the 
anterior  nerve-roots.  Between  the  posterolateral  groove  and 
the  posterior  fissure,  in  the  cervical  region,  exists  a  slight  fissure, 
called  the  postero-intermediate  fissure. 

The  gray  matter  consists  of  a  spongy  and  a  gelatinous  portion. 
The  former  includes  the  anterior  and  posterior  horns,  and  con- 
sists of  a  network  of  nerve-fibers  and  neuroglia  tissue,  among 
which  exists  a  large  number  of  nerve-cells  ;  the  latter  surrounds 
the  heads  of  the  posterior  horns  and  forms  a  layer  around 
the  central  canal.  The  gray  matter  is  completely  surrounded  by 
the  white  matter,  save  at  the  apex  of  the  posterior  horns.  It  is 
divided  into  three  somewhat  irregular  extensions,  or  cornua, — 
anterior,  lateral,  and  posterior, — and  an  intermediate  portion,  or 
body.  The  anterior  extensions  or  horns  form  the  larger  part  of 
the  gray  matter;  in  general  they  are  shorter,  much  broader,  and 
more  irregular  than  are  the  posterior  horns,  and  do  not  reach 
the  ventral  periphery  of  the  cord.  They  contain,  particularly  in 
the  cervical,  and  lumbar  regions,  large  collections  of  multipolar 
nerve-cells,  variously  grouped.  The  lateral  horns  exist  through- 
out the  cervical  and  upper  dorsal  regions  as  well  as  in  the 
sacral  cord.  In  the  cervical  reo^ion,  near  the  base  of  the  lateral 
and  anterior  horns,  is  found  a  special  collection  of  multipolar 
cells,  whose  neuraxones  form  the  root-fibers  of  the  spinal  acces- 
sory nerve  on  each  side. 

The  posterior  horns  are,  in  general,  longer  and  much  narrower 
than  are  the  anterior.  They  taper  almost  to  a  point  near  the 
dorsal  periphery  of  the  cord,  and  are  enabled  to  reach  the  sur- 
face by  a  dipping-in  of  small  processes  of  neuroglia  tissue. 
They  diverge  slightly,  this  divergence  being  most  marked  in 
the  cervical  region.  Each  horn  is  divided  into  a  narrow  part,  or 
neck,  "cervix  cornu,"  and  an  expanded  part,  or  head,   "caput 


SPINAL  CORD. 


73 


cornu."  Near  the  tip  of  the  head  of  each  posterior  horn  exists 
a  layer  of  semitransparent  glassy  material,  which  forms  a  cap  to 
the  cornu,  and  is  called  the  substantia  gelatinosa  of  Rolando. 
It  extends  throughout  the  entire  cord  and  into  the  medulla, 
where  it  becomes  markedly  increased  in  amount,  contains  a 
large  number  of  nerve-cells,  and  forms  one  of  the  end  stadons 


-~r  COi 


Fig.  40. — Transverse  Section  of  the  Human  Spinal  Cord  at  the  Level  of  the 
Eighth  Dorsal  Vertebra.     X  10. — {Landois  and  Stirling.) 

s.a.  Anterior  longitudinal  fissure,  s.p.  Septum  posterium.  c.a.  Anterior  commissure,  s.g.c. 
Substantia  gelatinosa  centralis,  c.c.  Central  canal,  c:/'.  Posterior  commissure,  w.  Vein. 
cro.a.  Anterior  horn.  coJ.  Lateral  horn,  and  behind  it  the  processus  reticularis,  co.^. 
Posterior  horn.  a.  Anterolateral,  d.  Anteromedian  group  of  ganglionic  cells,  c:  Cells 
of  the  lateral  horn.  d.  Cells  of  Clarke's  column,  e.  Solitary  cells  of  the  posterior  horn. 
r.a.  Anterior  root.  i:p.  Posterior  root,  with  /  its  bundle  of  fibers.  /''.  Postero-internal 
bundle,  f''^.  Longitudinal  fibers  of  the  posterior  cornu.  s.g.R.  Gelatinous  substance  of 
Rolando,     /.a.  Anterior  column,    f.l.   Lateral  column.     //.  Posterior  column. 


for  the  sensory  division  of  the  fifth  or  trigeminal  nerve.  This 
substantia  gelatinosa  Rolandi  was  formerly  believed  to  be  com- 
posed simply  of  a  rich  network  of  neuroglia  fibers  and  cells,  but 
it  has  been  shown  by  the  recent  researches  of  Weigert  that  this 
substance  is  poor  in  neuroglia  tissue.     It    contains    numerous 


74  CENTRAL  NERVOUS  SYSTEM. 

small  multipolar  nerve-cells,  whose  nciiraxones  pass  into  the 
adjoining  part  of  the  lateral  columns.  Koelliker  has  shown  that 
many  collaterals  from  the  posterior  nerve-roots  pass  through  the 
substantia  gelatinosa  on  their  way  toward  the  anterior  cornu, 
while  others  terminate  about  the  cells  existing  in  the  posterior 
cornu.  Froni  the  caput  cornu  they  taper  in  the  way  described 
above,  reaching  the  surface  of  the  cord,  and  are  called  the 
"apices  cornuum  posteriores." 

Between  the  bases  of  each  anterior  and  posterior  horn  there 
is  an  extension  of  the  intermediate  gray  substance  into  the 
white  matter  in  the  form  of  a  dense  interlacement  of  fibers.  This 
is  the  processus  reticularis,  well  marked  in  the  cervical  and 
upper  dorsal  regions. 

The  intermediate  gray  substance,  or  that  portion  of  the  gray 
matter  between  the  anterior  and  posterior  cornua,  often  termed 
the  middle  zone,  consists  of  a  network  of  neuroglia  tissue, 
ner\^e-fibers,  isolated  nerve-cells  and  their  processes,  blood- 
vessels, and  lymphatics. 

Connecting  the  gray  matter  of  the  lateral  halves  of  the  cord 
exist  two  commissures — the  anterior,  or  white,  and  the  poste- 
rior, or  gray. 

The  central  canal  is  situated  in  the  gray  commissure  and 
extends  throughout  the  entire  length  of  the  spinal  cord,  ending 
in  the  filum  terminale.  As  the  cord  merges  into  the  medulla, 
the  canal  trends  backward,  and  finally  opens  into  the  fourth 
ventricle.  In  the  conus  medullaris  it  is  more  dorsally  located, 
becomes  widened,  and  forms  the  ventriculus  terminalis  of 
Krause.  In  transverse  sections  it  appears  oval  or  circular,  and 
is  surrounded  by  neuroglia  tissue — the  substantia  gelatinosa  cen- 
tralis of  Stilling.  It  is  lined  with  cylindric  epithelium,  which 
in  the  embryonic  cord  bear  cilia.  The  epithelial  cells  have 
basal  processes  which  are  continuous  with  the  neuroglia  tissue 
upon  which  they  rest.  This  canal  is  the  remains  of  the  neural 
or  epiblastic  canal  of  the  embryo.  In  the  adult  it  is  filled  with 
disintegrated  products  of  the  lining  epithelium,  the  epithelial 
cells  having  lost  their  cilia. 

The  anterior  or  white  commissure  forms  the  floor  of  the 
anterior  median  fissure.     It  is  composed  of  obliquely  decussat- 


SPINAL  CORD. 


75 


ing  medullated  nerve-fibers,  neuraxones  from  the  intrinsic  cells 
of  the  gray  matter,  which  cross  over  and  enter  the  anterior  and 
anterolateral  areas  of  the  opposite  side  of  the  cord.  It  contains, 
in  addition,  neuraxones  from  the  median  cell  groups  of  the  ante- 
rior horns,  and,  lastly,  collateral  branches  from  the  fibers  of  the 
direct  pyramidal  tracts  which  cross  and  probably  end  about  the 
motor  cells  of  the  opposite  side.  According  to  Bechterew, 
fibers  pass  from  the  ventral  part  of  each  lateral  column,  via  the 
anterior  commissure,  to  the  ventral  column  of  the  opposite  side, 


Fjg.  41. — Section  of  the  Isthmus  of  the  Lumbar  Cord.  Showing  the  central  canal 
in  the  middle,  surrounded  by  the  substantia  gelatinosa  centralis. — {^After  E.  A.  Scha/er, 
from  Qtiain.) 

J.  a.  Anterior  median  fissure,  p.  m.  c.  Posterior  white  column,  a.  c.  Anterior  white  commis- 
sure. 

The  posterior  or  gray  commissure  contains  the  central  canal 
and  connects  the  posterior  horns.  It  is  made  up  of  medullated 
nerve-fibers,  which  run  transversely  or  obliquely.  Between  the 
fibers  exists  a  large  amount  of  neuroglia  tissue,  which  gives  to  it 
its  gray  color.  The  fibers  of  the  posterior  commissure  represent 
collateral  branches  of  the  posterior  nerve-roots,  which  cross  over 
to  the  opposite  side.  It  also  contains  neuraxones  from  cells  exist- 
ing in  the  posterior  horns,  which  pass  over  to  the  opposite  side. 


76  CENTRAL  NERVOUS  SYSTEM. 

THE    NERVE-CELLS    OF   THE    CORD. 

In  the  gray  matter  of  the  cord  there  exists  a  variety  of  forms 
of  multipolar  nerve-cells.  They  may,  in  general,  be  divided  into 
two  classes,  corresponding  to  the  types  of  Golgi — viz.,  those 
cells  whose  neuraxones,  although  giving  off  collaterals,  retain 
their  individuality  and  are  usually  of  great  length.  These  belong 
to  Golgi's  first  type  of  cells ;  those  whose  neuraxones  are  short, 
soon  divide  and  subdivide  into  fine  ramifications,  and  do  not 
leave  the  gray  matter — Golgi's  second  type  of  cells. 

Another  classification,  more  in  accordance  with  their  supposed 
functions,  is  as  follows:  (i)  The  motor,  ganglionic,  or  trophic 
cells  ;  (2)  the  intrinsic  cells  ;  and  (3)  the  reflex  cells. 

The  motor  cells  differ  from  the  others  in  size,  being  the 
largest  cells  of  the  cerebrospinal  axis.  They  are  irregular  in 
form,  and  possess  a  very  large  number  of  offshoots,  or  den- 
drites, which  branch  repeatedly.  They  are  located  in  the  an- 
terior cornua,  throughout  the  whole  extent  of  the  spinal  cord, 
and  their  neuraxones  form  the  anterior  nerve-roots.  These  cells, 
with  their  neuraxones  and  dendrites  and  the  motorial  end  plates, 
form  the  peripheral  motor  neurones,  or  neurones  of  the  first  order. 

Two  important  groups  of  motor  cells  are  found  most  marked 
in  the  cervical  and  lumbar  enlargements,  but  extending  through- 
out the  entire  extent  of  the  cord — viz.,  an  anteromedian  and  pos- 
terolateral group  (Fig.  43).  The  researches  of  Kaiser  have  thrown 
considerable  light  upon  the  exact  anatomic  grouping  of  the  cells 
in  the  anterior  cornua  of  the  cervical  recjion.  The  followintr  four 
groups  have  been  described  by  him  :  First,  a  group  just  anterior 
to  the  origin  of  the  lateral  horns  and  extending  into  those  horns. 
This  group  extends  downward  as  far  as  the  sixth  cervical  seg- 
ment. It  is  called  the  accessory  nucleus,  and  gives  origin  to  the 
spinal  accessory,  or  eleventh  pair  of  cranial  nerves.  Secondly, 
a  group  of  cells  on  either  side  exists  at  the  exit  of  the  first  cer- 
vical nerve,  and  on  the  internal  surface  of  the  anterior  horn 
near  its  base.  This  group  continues  upward  into  the  medulla, 
and  there  gives  origin  on  each  side  to  the  hypoglossal  or  twelfth 
pair  of  cranial  nerves.  A  third  group  is  known  as  the  middle 
or  mesial  group,  and  is  located  in  the  middle  of  the  base  of  the 


'^^^^' 


^x; 


i 


/^■^■^■w"' 
4/i,^. 


/ 


£i"'^'' 


j^W' 


r 


■w 


Fig.  42. — A  Group  of  Multipolar   Nerve-cells   from   an   Anterior  Horn  of  the 
Spinal  Cord.     Showing  Nissl  granules  and  pigment. 

77 


SPINAL  CORD. 


79 


anterior  horn  of  each  side.  This  cell  group  extends  throughout 
the  entire  cord.  It  is  particularly  well  marked  in  quadrupeds 
whose  dorsal  muscles  are  well  developed,  and  therefore  has 
been  termed  by  Kaiser  the  nucleus  for  the  back  muscles.  The 
fourth  group  is  found  along  the  lateral  periphery  of  the  anterior 
horn,  having  a  vertical  extent  from  the  fourth  cervical  to  the  upper 
part  of  the  second  dorsal  segment.  This  is  the  area  from  which 
the  nerves  of  the  brachial  plexus  are  derived.  This  group  has 
been  called  by  Kaiser  the  cell  group  for  the  upper  extremity. 


Fig.  43. — Section  of  the  Lumbar  Cord  of  an  Adult.     Showing  the  anteromedian  and 

posterolateral  groups  of  cells. 

All  these  cells  are  motor  in  function,  innervating  the  muscles 
to  which  the  anterior  nerve-roots  are  destined.  They  also  have 
a  very  important  bearing  upon  the  nutrition  of  the  anterior 
nerve-roots  and  the  muscles  which  those  nerves  innervate. 
Any  acute  pathologic  change  in  the  cells  is  followed  by  motor 
paralysis,  partial  or  complete,  degeneration  of  the  motor  nerve- 
fibers,  and  rapid  wasting  of  the  muscles  to  which  they  are  dis- 
tributed. They  are,  therefore,  trophic  as  well  as  motor  in  func- 
tion. These  cells  are  functionally  grouped,  according  to  certain 
definite  movements  associating  groups  of  muscles. 


So 


CENTRAI,  NERVOUS  SYSTEM. 


Tlic  intrinsic  cells  arc  fountl  distributed  throughout  that  part 
of  the  gray  matter  located  between  the  anterior  and  posterior 
cornua,  the  so-called  middle  zone.  The  neuraxones  of  the  intrinsic 
cells  pass  into  the  white  columns  of  the  same  and  opposite  sides, 
as  long  and  short  fibers,  where  they  divide  T-shaped,  one  branch 
passing  upward,  the  other  downward.  The  long  fibers  are  doubt- 
less sensory.  The  short  fibers  are  probably  associative  in  func- 
tion, passing  upward  and  downward  in  the  white  columns  of  the 


/  ^/ 


^^  ^  KM 


te;^^45l/^ 


Fui.  44. — Camera  Lucida  Drawing  of  a  Part  of  an  Anterior  Horn  with  Adjacent 
White  Matter  of  the  Lateral  Column.  Showing  nerve-fibers  coining  from  that 
column  and  coursing  between  and  around  the  motor  nerve-cells.  Stained  after  method  of 
Weigert-Pal. 

cord,  giving  off  collaterals  which  reenter  the  cord  at  higher  and 
lower  levels,  ending  in  brush-like  expansions  about  the  intrinsic 
cells  of  those  levels.  A  group  of  intrinsic  cells  exists  near  the 
base  of  each  anterior  horn,  the  neuraxones  of  which  pass  ob- 
liquely across  the  gray  and  white  matter,  becoming  vertical  near 
the  periphery  of  the  opposite  side  of  the  cord,  forming  the  antero- 
lateral ascending  tract  of  Gowers.  This  tract  is  probably  sen- 
sory in  function,  transmittijig  to  the  brain  impulses  of  pain  and 
temperature.    A  second  group  of  these  cells  is  located  at  the 


^' 


V 


VI 


\^ 


VII 


IX 


VIII 


Fig.  45. — Diagram  of  a  Transverse  Section  of  the  Spinal  Cord. — i^After  Starr.) 
On  the  right  side  the  columns  of  the  cord  are  shown,  and  the  fibers  entering  the  gray  matter 
from  these  columns.  I.  Anterior  median  column.  II.  Anterolateral  column.  III. 
Lateral  limiting  layer.  IV.  Ascending  anterolateral  tract  of  Gowers.  V.  Direct  cerebellar 
column.  VI.  Crossed  pyramidal  column.  VII.  Lissauer's  column.  VIII.  Column  of 
Burdach.  IX.  Column  of  Goll. 
The  posterior  nerve-roots  are  shown  on  the  right  side  of  the  diagram,  and  their  various  methods 
of  termination  in  the  gray  matter :  I.  Fiber  entering  Lissauer's  tract.  2.  Fiber  entering 
posterior  horn.  3.  Fiber  terminating  deep  within  posterior  horn.  4.  Fiber  entering 
column'  of  Burdach.  5.  Fiber  passing  to  root  zone  of  column  of  Burdach,  and  sending 
the  collateral  fiber  to  the  anterior  horn.  6.  Fiber  entering  root  zone,  and  sending  collateral 
to  the  Clarke  column  of  cells.  7.  Fiber  entering  root^zone  and  passing  by  way  of  the  gray 
commissure  to  the  opposite  side  of  the  cord. 
On  the  left  side  the  various  cells  of  the  gray  matter  are  shown  :  a.  Motor  cells,  with  motor 
nerve-roots  passing  out  of  the  cord.  b.  Intrinsic  cells  of  the  posterior  horns ;  the  one  on 
the  margin  is  a  "  border-cell  ";  the  other  lies  deep  within  the  horn;  they  send  neuraxones 
into  the  posterior  and  lateral  columns  respectively,  c.  Intrinsic  cell  of  the  posterior  horn  ; 
Golgi's  second  type.  d.  Cell  of  the  column  of  Clarke,  with  its  axone  passing  to  the  direct 
cerebellar  column,  e.  Intrinsic  cells  of  the  intermediate  gray  matter,  with  their  axones 
passing  into  the  anterolateral  column,  f.  Intrinsic  cell  in  median  gray  matter,  with  its 
axone  passing  to  Gowers'  tract,  g.  Commissural  cells  in  the  median  gray  matter,  their 
axones  passing  to  the  opposite  side  of  the  cord.  h.  Sensory  cell  sending  its  axone  to 
opposite  column  of  Gowers. 

6  81 


SPINAL  CORD.  83 

base  of  the  posterior  horn,  near  its  inner  side,  close  to  the 
posterior  commissure.  They  are  of  large  size,  multipolar,  and 
sensory  in  function.  Spread  about  them  exist  the  end  brushes 
of  collaterals  and  axones  from  the  posterior  nerve-roots,  which 
conduct  impressions  of  equilibrium  from  the  trunk  muscles  to 
these  cells.  From  this  group  of  cells  neuraxones  pass  horizon- 
tally across  the  gray  and  white  matter  of  the  same  side,  becoming 
vertical  along  the  periphery  of  the  cord,  where  they  form  the 
direct  cerebellar  tract,  or  column  of  Flechsig.  They  extend  from 
the  third  lumbar  to  the  seventh  cervical  nerve.  This  entire 
group  of  cells  forms  the  vesicular  column  of  Lochart  Clarke. 
Cells  of  a  like  character  exist  in  the  same  location  throughout 
the  sacral  region,  and  have  been  termed  the  sacral  nucleus  of 
Stilling.  Among  the  intrinsic  cells  may  be  mentioned  a  group 
of  cells  on  each  side  located  near  the  median  surface  of  the  base 
of  the  anterior  horns — the  so-called  commissural  cells.  They 
possess  axones  which  have  both  a  short  and  long  course,  those  of 
short  course  passing  in  curves  through  the  anterior  commissure 
into  the  opposite  anterior  cornu,  where  each  axone  terminates 
by  breaking  up  into  two  or  three  fine  filaments.  They  probably 
associate  in  function  the  two  anterior  cornua.  The  axones  having 
a  long  course  pass  via  the  anterior  commissure  through  the 
gray  matter  into  the  anterolateral  area  of  the  cord.  They  may 
conduct  sensory  impressions  to  the  opposite  side  of  the  cord. 
The  remaining  cells  belong  to  the  second  type  of  Golgi ;  they 
are  small,  spheric  or  triangular,  and  exist  mostly  In  the  posterior 
horns.  Their  axones  are  short  and  do  not  leave  the  gray 
matter;  they  divide  dichotomously,  breaking  up  into  a  network 
of  fine  filaments.     They  may  possibly  serve  a  reflex  function. 

The  white  matter  of  the  cord  surrounds  the  gray  matter  on 
all  sides  except  where  the  posterior  horns  reach  the  dorsal  peri- 
phery of  the  cord.  Macroscopically,  it  consists  of  a  homogeneous 
white  mass,  which,  when  examined  with  a  low  power  of  the 
microscope,  resolves  itself  into  masses  of  cut-off,  medullated 
nerve-fibers  arranged  vertically.  These  nerve-fibers  differ  very 
much  as  to  size,  and  have  no  neurilemma  or  sheath  of  Schwann. 
Between  the  nerve-fibers  exists  neuroglia  tissue  and  many 
fine  collaterals.     A  mantel  of  neuroglia,  the  subpial  neuroglia 


84  CENTRAL  NERVOUS  SYSTEM. 

layer,  surrounds  the  periphery  of  the  cord.  The  neurogHa 
gives  support  to  the  nerve-fibers  and  to  the  numerous  blood- 
vessels which  are  given  off  from  all  portions  of  the  periphery 
and  ramify  toward  the  center  of  the  cord. 

The  fibers  are  variable  in  size,  usually  corresponding  in 
diameter  to  the  length  of  the  tracts  to  which  they  belong. 

The  white  substance  is  divided  anatomically  into  three  primary 
columns  for  each  side — an  anterior  or  ventral,  a  lateral,  and  a 
posterior  or  dorsal.  The  anterior  column  lies  between  the 
anterior  cornua  and  ventral  nerve-roots.  The  lateral  columns 
are  between  the  exit  of  the  anterior  and  posterior  nerve-roots. 
The  posterior  columns  are  situated  between  the  posterior  cornua 
and  nerve-roots,  being  separated  from  each  other  by  the  dorsal 
median  septum.  They  are  subdivided  by  the  intermediate 
neuroglia  septum  into  two  smaller  columns — an  inner  or 
median  one,  adjacent  to  the  posterior  median  fissure,  called 
the  column  of  GoU,  and  an  outer  or  external  one,  located 
between  the  septum  and  the  posterior  horn,  called  the  column 
of  Burdach  or  the  posterior  root  zone.  It  is  to  be  noted  that 
this  intermediate  septum  is  only  well  marked  in  the  cervical 
region,  but  the  columns  are  distinct  throughout  the  cord. 
These  various  columns  are  further  subdivided  into  a  number  of 
tracts  or  fasciculi  of  nerve-fibers,  long  and  short,  whose  ana- 
tomic and  physiologic  relations  have  been  made  known  by 
pathologic  and  embryologic  research.  The  fibers  which  com- 
pose these  tracts  spring  from  four  different  sources  :  First,  from 
the  posterior  nerve-roots  and  spinal  ganglia,  having  a  centri- 
petal course  ;  second,  fibers  from  the  motor  area  of  the  brain, 
centrifugal  in  their  course  ;  third,  fibers  which  pass  into  the  white 
matter  of  the  cord  from  the  intrinsic  cells  of  the  gray  matter, 
which  form  long  and  short  tracts,  the  long  tracts  being  doubt- 
less sensor)'  in  character,  while  the  short  tracts  are  supposed 
to  associate  different  levels  of  the  gray  matter ;  and  fourth, 
fibers  having  a  descending  course:  the  neuraxones  from  the 
Purkinje  cells  of  the  cerebellar  cortex. 

We  have  thus  found  that  the  white  matter  which  appeared  to 
the  naked  eye  as  a  homogeneous  mass  may  be  resolved  into 
vertical  fibers  grouped  into  tracts  whose  course  may  be  long  or 


Fig.  46. — MiCROPHOTOGRAPH  OF   Transverse  Section  of   Cord.     Showing  nerve-fibers 

cut  across. 

85 


SPINAL  CORD. 


87 


short.  Our  knowledge  In  regard  to  the  exact  location  of  the 
different  systems  of  these  tracts  has  been  greatly  aided  by  the 
study  of  secondary  degeneration,  the  result  of  experimental  or 
pathologic  destruction  of  partial  or  total  transverse  sections 
of  the  cord.  This  study  was  undertaken  by  Turck,  who  inves- 
tigated the  after-effects  of  such  sections  of  the  cord.  He  found 
that  when  the  cord  was  completely  destroyed  transversely  by  a 


Fig.  47. — MiCROPHOTOGRAPH    OF   A    PARTIAL   TRANSVERSE   SECTION    OF   THE    WhITE 

Matter  of  the  Spinal  Cord  of  an  Ox. 


lesion, — such  as  transverse  myelitis,  hemorrhage,  or  the  like, — 
certain  definite  tracts  or  systems  of  fibers  degenerate  upward 
or  centripetally,  while  others  degenerate  downward  or  centri- 
fugally.  The  study  of  secondary  degeneration  was  long  ago 
carried  out  by  Waller,  who  showed  that  if  a  nerve  were  severed 
from  its  mother  cell,  it  would  degenerate  throughout  its  whole 
extent,  the  degeneration  usually  being  in  the  direction  in  which 
the  nerve-fiber  conducted  impulses.    For  example,  if  an  anterior 


S8 


CENTRAL   NKRVOUS  SYSTEM. 


ncrve-root  be  severed  from  its  connection  with  its  trophic  cell 
in  the  anterior  horn  of  the  spinal  cord,  that  nerve  degenerates 
peripherally  to  its  termination  in  the  muscle  which  it  innervates, 
the  muscle  sharing  in  the  resulting  atrophy.  Also  on  section 
of  a  posterior  or  sensory  root,  ventrad  to  its  ganglion,  which 
contains  its  trophic  cell,  that  nerve  degenerates  centrally  or  in 
the  direction  in  which  it  conducts  impulses.     On  the  contrary, 


Fig.  48. — SciiKMATic  Representation  of  the  Situ.vtion  of  the  Various  Tracts  of 
Fibers  in  the  Spinal  Cord. 

I.  Direct  pyramidal  tract.  II.  Descending  tract  of  Marchi  and  Lowenthal.  III.  Olivary  or 
triangular  tract.  IV.  Anterolateral  ground  bundles  of  fibers.  V.  Anterolateral  ascending 
tract  of  Cowers.  VI.  Lateral  limiting  layer.  VII.  Direct  cerebellar  tract.  VIII.  Crossed 
pyramidal  tract.  IX.  Lissauer's  tract.  X.  Middle  root  zone.  XL  Posterior  root  zone. 
XII.  Posterointernal  or  column  of  Coll.  XIII.  Septomarginal  tract.  XIV.  Comma  tract 
of  Schultze.     XV.   Anterior  root  zone.      XVI.   Cornu  commissural  tract. 


if  a  section  be  made  dorsal  to  the  ganglion,  the  nerve  degener- 
ates peripherally  throughout  its  whole  extent  in  a  direction 
opposite  to  that  in  which  impulses  are  conducted.  A  careful 
study  has  shown  that  the  following  tracts  in  the  spinal  cord 
undergo  secondar)^  degeneration — viz.,  the  direct  and  crossed 
motor  tracts,  the  tracts  of  the  columns  of  Burdach  and  Goll,  the 
direct  cerebellar,  the  anterolateral  ascending  tract  of  Gowers, 
and  the  descending  tract  of  Marchi  and  Lowenthal.     It  is  in- 


SPINAL  CORD. 


teresting  to  note  that  the  embryologic  studies  of  Plechsig, 
Bechterew,  Edinger,  and  Kahler  have  confirmed  the  separate 
existence  of  these  tracts  and  have  proved  that  other  tracts  also 
are  found  in  the  cord.  Flechsig  has  shown  that  the  different 
tracts  of  the  white  matter  receive  their  myehn  at  certain 
definite  periods  of  embryonic  development.  In  early  embryonic 
life  that  part  of  the  cord  which  afterward  consists  of  white 
matter  is  composed  entirely  of  naked  axis-cylinders,  which  gives 
to  a  section  a  dark  gray  appearance.  Later,  as  the  tracts  be- 
come medullated,  they  can  easily  be  distinguished  by  the  white 
appearance  which   each  tract    assumes.      By   this    method,   the 

following  tracts  or  systems  of  fibers  have  been  differentiated 

viz.,  the  gro^id  bundles  of  the  anterior  columns,  ground Jjundles 
of  the  posterior  columns,  the  anterolateral  mixed  zones,  the 
lateral  limiting  layers,  the  columns  of  Goll,  the  direct  cerebellar 
tracts,  the  direct  and  crossed  pyramidal  tracts,  the  anterolateral 
ascending  tracts  of  Gowers.* 

In  order  to  render  clearer  the  anatomic  relations  of  the  sep- 
arate tracts,  it  will  be  necessary  to  accurately  describe  the  rela- 
tive positions  of  these  tracts  as  seen  on  transverse  section. 

The  anterior  or  direct  pyramidal  tracts  or  colwmis  of  Turck 
form  narrow  columns  of  nerve-fibers  bordering  on  each  side  of 
the  anterior  median  fissure.  These  tracts  extend  downward  in 
the  cord,  gradually  decreasing  in  size,  and  usually  terminate  at 
the  mid-dorsal  region.  In  rare  instances,  when  a  larger  per- 
centage than  normal  of  the  motor-fibers  take  this  direct  course,  . 


*  I.   The  ground  bundles  of  the  anterior  columns  receiveftheir  myelin  when  the  fetus  is  from 
30  to  32  cm.  long.      About  the  sixth  month. 

2.  The  ground  bundles  of  the  posterior  columns,  when  the  fetus,ds'25  cm.  in  length.   About 
the  fifth  month. 

3.  The  anterolateral  mixed  zone,  when  the  fetus  is  25  to  35  cm.  long.     Fifth  to   seventh 
month. 

4.  Lateral  limiting  layer,  when  the  fetus  is  32  cm.  long.     About  the  sixth  month. 

5.  The  fasciculi  of  the  columns  of  Goll  receive  their  myelin  when  the  embryo  is  between 
six  and  seven  months  old. 

6.  The  direct  cerebellar  tracts  receive  their  white  substance  about  the  seventh  month  of 
fetal  life. 

7.  The  fibers  of  the  direct  and  crossed  pyramidal  tracts  become  enveloped  in  myelin  at 
about  the  ninth  month. 

8.  The  anterolateral  ascending  tracts  of  Go.wers  become  medullated  at  the  eighth  month 
of  embryonic  life. 


90  CENTRAL  NERVOUS  SYSTEM. 

tliey  continue  ilownward  as  far  as  the  luml)ar  or  sacral  region, 
and  rxtcnil  from  the  white  commissure  to  the  periphery  of  the 
cord,  causing  shght  bulgings  on  each  side  of  the  anterior  median 
fissure,  (^n  the  otlicr  liand,  when  the  cohmins  contain  less  than 
the  normal  number  of  fibers,  they  terminate  about  the  middle  of 
the  cervical  region. 

The  autcrior  ground  bundles  of  FlecJisig  comprise  all  that 
part  of  the  anterior  columns  outside  of  the  direct  pyramidal 
tracts.  They  extend  throughout  the  entire  length  of  the  cord, 
and  consist  chiefly  of  fibers  having  a  short  course,  which  fibers 
doubtless  connect  different  levels  of  the  anterior  cornua. 

The  anterolateral  mixed  zone,  one  on  each  side,  is  bounded 
on  its  inner  side  by  the  gray  matter  ;  externally,  by  Gowers' 
tract  and  the  crossed  pyramidal  tract.  The  posterior  portions 
of  these  columns  bordering  upon  the  intermediate  gray  matter 
and  the  posterior  horns  are  called  the  lateral  limiting  layers. 
This  zone  is  composed  of  association  fibers  which  probably  con- 
nect different  levels  of  the  gray  matter. 

The  anterolateral  ascending  tracts  of  Gowers  occupy  rather 
long,  narrow,  crescentic  areas  along  the  anterolateral  periphery 
of  the  cord  in  front  of  the  direct  cerebellar  and  crossed  pyra- 
midal tracts,  and  are  found  throughout  the  cord  as  low  down  as 
the  lumbar  enlareement. 

The  anterolateral  descending  tracts  of  Marchi  and  Lozuen- 
thal  comprise  a  small  area  in  Gowers'  column  of  each  side,  close 
to  the  periphery  of  the  cord.  These  areas  were  discovered  by 
Marchi  and  Lowenthal.  They  have  been  found  to  extend 
throughout  nearly  the  entire  length  of  the  cord. 

The  direct  cerebellar  tract, — also  called  the  column  of  Flech- 
sig. — one  for  each  side,  exists  along  the  periphery  of  the 
lateral  column,  posterior  to  the  tract  of  Gowers  and  external  to 
the  crossed  pyramidal  tract.  In  the  upper  cervical  region  its 
posterior  part  is  separated  from  the  periphery  of  the  cord  by 
the  crossed  pyramidal  tract.  It  originates  as  low  down  as  the 
first  lumbar  nerve,  and  has  its  greatest  size  where  the  cells  of 
Lockhart  Clarke,  whose  neuraxones  form  the  greater  portion  of 
this  tract,  are  best  developed — namely,  in  the  dorsal  region. 

Ihe  crossed  motor  or  pyramidal  tracts — the  fasciculi  cerebro- 


SPINAL  CORD.  gi 


spinalis  lateralis — occupy  a  large  area  in  the  posterior  part  of  the 
lateral  columns  of  each  side.  They  extend  throughout  the 
entire  length  of  the  cord,  some  of  their  fibers  terminating  in  the 
conus  medullaris.  Through  the  greater  part  of  the  cervical  and 
dorsal  regions  these  tracts  are  separated  from  the  periphery  of 
the  cord  by  the  cerebellar  tracts.  In  the  upper  cervical  and  lower 
dorsal  regions,  owing  to  a  movement  ventrad  of  the  direct 
cerebellar  tracts,  the  motor  tracts  are  permitted  to  reach  the 
periphery  of  the  cord,  which  position  they  retain  throughout  the 
lumbar  region.  Their  posterior  surfaces  are  in  contact  with  the 
posterior  horns  ;  their  anterior  portion,  with  the  tracts  of 
Gowers  and  the  lateral  limiting  layers. 

The  posterior  columns  contain  two  chief  systems  of  fibers  or 
tracts,  which  extend  throughout  the  cord,  being  separated  from 
each  other  in  the  dorsal  and  cervical  regions  by  a  process  of 
neuroglia  called  the  intermediate  septum.  On  each  side  the 
outer  area,  which  borders  on  the  posterior  horn,  is  called  the 
column  of  Burdach,  posterior  ground  bundle  of  Flechsig,  or  the 
posterior  root  zone  of  Charcot.  The  inner  fasciculus  or  bundle 
of  fibers,  which  borders  upon  the  posterior  median  fissure,  is 
called  the  column  of  Goll,  or  postero-internal  column. 

The  origin  and  partial  course  of  the  fibers  which  compose  the 
various  tracts  of  the  cord  will  be  described  in  the  order  of  their 
relative  importance  from  a  clinical  and  physiologic  standpoint. 

T/ie  Crossed  and  Direct  Pyramidal  Tracts. — The  motor  fibers 
of  the  cord  which  are  located  in  the  direct  and  crossed  pyra- 
midal tracts  arise  from  the  motof  areas  of  the  brain,  and  repre- 
sent the  neuraxones  of  the  large  pyramidal  cells,  which  are 
abundandy  found  in  the  third  layer  of  the  cortex.  Their 
course  from  the  cerebral  cortex  to  the  medulla  will  be  de- 
scribed later.  When  they  reach  the  medulla  they  occupy  a 
large  area  on  each  side  of  the  anterior  median  fissure,  and  at  the 
first  or  second  cervical  nerves  large  bundles  of  fibers  or  axones, 
representing  about  eighty  per  cent,  of  the  whole  number,  pass 
obliquely  across  to  the  opposite  side,  entering  the  posterior  part 
of  the  lateral  column  of  the  cord ;  hence  the  name  "  crossed 
pyramidal  tract."  These  crossed  fibers  become  verdcal  and 
extend  downward,  gradually  decreasing  in  size  undl  they  reach 


92  CEMKAI.  NERVOUS  SYSTEM. 

their  termination,  at  the  level  of  the  third  or  fourth  sacral  nerve, 
a  small  number  of  fibers  continuing  downwarti  to  terminate  in 
the  fihim  terminale.  The  neuraxones  which  do  not  cross, 
representing  about  twenty  per  cent,  of  the  motor  fibers,  pass 
downward  in  the  area  of  the  cord  adjacent  to  the  anterior 
median  fissure  on  the  same  side ;  hence  they  are  called  the 
direct  or  uncrossed  pyramidal  tract.  They  usually  cease  about 
the  level  of  the  mid-dorsal  region.  The  motor  neuraxones,  like 
most  of  the  long  fibers  of  the  columns  of  the  cord,  give  off  at 
different  levels  side  branches  or  collaterals  which  leave  the 
parent  stem  at  right  angles.  The  axones,  with  the  collaterals 
composing  the  crossed  pyramidal  tract  of  each  side,  pass  for- 
ward and  inward,  entering  the  gray  matter,  where  they  break 
up  about  the  motor  nerve-cells  into  innumerable  fine  filaments 
or  arborizations. 

The  neuraxones  and  collaterals  of  the  direct  pyramidal  tract 
end,  according  to  Lenhossek,  in  fine  brush-like  expansions  about 
the  motor  nerve-cells  of  the  anterior  horn  of  the  same  side. 
On  the  contrary,  undoubted  clinical  and  experimental  evidence 
is  at  hand  to  prove  that  the  greater  portion  of  fibers  cross  over 
through  the  anterior  commissure  to  end  about  the  motor  cells 
existing  in  the  opposite  anterior  cornu.  Most  of  the  fibers  of 
the  direct  pyramidal  tract  seem  destined  to  the  arm  ;  hence  the 
relation  of  the  arm  is  almost  exclusively  with  the  cerebral  hemi- 
sphere of  the  opposite  side.=-=  The  fibers  of  the  motor  tracts, 
direct  and  crossed,  conduct  impulses  of  voluntar)^  motion  from  the 
motor  areas  of  the  brain  to  the  muscles.  If  the  fibers  of  the  motor 
tract  be  destroyed  by  severing  their  connection  with  the  cells  of 
the  motor  area  of  the  brain,  there  will  result  a  motor  paralysis 
of  the  opposite  side  of  the  body  and  a  descending  degenera- 
tion from  the  point  of  lesion  throughout  the  entire  extent 
of  the  tract.  In  the  cord  the  degenerated  areas  will  be 
the  direct  pyramidal  tract  of  the  same,  and  the  crossed  pyra- 
midal tract  of  the  opposite  side.  This  degeneration  is  com- 
plete, involving  the  termination  of  the  axones  and  collaterals 


*W.  H.  B.  Stoddart  has  proven  by  experimental  division  of  an  anterior  pyramid  in  a 
number  of  dogs  that  nearly  all  the  fibers  of  the  direct  pyramidal  tract  ultimately  cross  to  the 
opposite  side  of  the  cord. 


Fig.  49.— Diagram  Indicating  the  Course  of  the  Motor  and  Sensory  Fibers 
OF  THE  Spinal  Cord  and  Medulla. 

,  a.  Motor  cells  of  the  cerebral  cortex,  b,  b.  Arborizations  of  the  fibers  of  the  sensory  tract 
in  the  cerebral  cortex,  c.  Nucleus  of  the  column  of  Burdach,  showing  terminal  arboriza- 
tions of  the  long  sensory  fibers  of  the  cord.  d.  Nucleus  of  the  column  of  Goll,  showing 
terminal  arborizations  of  the  long  sensory  fibers  of  the  cord.  e.  Section  of  the  medulla, 
showing  sensory  decussation.  /  Section  of  medulla,  showing  motor  or  pyramidal  decus- 
sation, g,  g.  Motorial  end  plates,  h.  Section  through  the  cervical  region  of  the  cord, 
showing  termination  in  the  anterior  horn  of  the  motor  fibers  of  the  direct  pyramidal  tract 
after  they  have  crossed  in  the  anterior  commissure ;  also  fiber  of  crossed  pyramidal  tract  end- 
ing about  anterior  horn  cell  of  same  side,  i,  i.  Posterior  spinal  ganglia.  /,  k.  Sensory  fibers 
of  short  course.  /.  Siensory  fibers  of  long  course,  terminating  in  medulla.  ;«,  771,  7/1.  Sen- 
sory end  organs,     n.  Section  through  lumbar  cord. 

93 


SPINAL  CORD.  95 

about  the  nerve-cells  of  the  anterior  cornua,  and  is  due  to 
the  loss  of  trophic  or  nutritional  influence  which  results  from 
the  severance  of  the  nerve-fibers  from  their  mother  cells  in 
the  motor  areas  of  the  cortex.  The  peripheral  portion  of  the 
tract,  on  the  contrary,  remains  normal,  because  its  nutrition  is 
dependent  upon  the  motor  cells  of  the  anterior  cornu,  whose 
neuraxones  form  the  peripheral  portion  of  the  tract* 


THE  COURSE    OF    FIBERS    IN    THE    SENSORY    TRACTS 

OF  THE  CORD. 

The  sensory  portion  of  the  cord  may  be  divided  into  four 
chief  areas  for  each  side — that  is,  the  direct  cerebellar  tracts,  the 
columns  of  Burdach  and  Goll,  and  Gowers'  anterolateral  ascend- 
ing tracts. 

The  dii^ect  cei'ebellar  tract,  or  the  fasciculus  cerebellospinalis, 
owes  its  origin  to  neuraxones  from  the  cells  of  the  vesicular 
column  of  Clarke. f  These  cells,  which  are  multipolar,  exist  at 
the  base  of  the  posterior  horn  near  its  inner  side,  and  form  a 
distinct  column,  vertical  in  extent  from  the  seventh  cervical  to 
the  third  lumbar  segment.  It  should  be  noticed,  however,  that 
Stilling  has  called  attention  to  a  number  of  cells  in  a  correspond- 
ing portion  of  the  cord  in  the  upper  cervical  and  lower  lumbar 
regions,  which  cells  probably  perform  a  similar  function,  so  that 
in  reality  the  column  may  be  said  to  extend  throughout  the 
cord.  From  this  column  of  cells  numerous  neuraxones  pass 
rather  obliquely  across  the  white  matter  of  the  lateral  column, 
reaching  the  circumference  of  the  cord,  dorsad  to  Gowers'  tract. 


*  In  many  of  the  lower  animals — i.  e.,  in  the  dog,  cat,  rabbit,  etc. — there  is  an  apparent  total 
decussation  of  the  motor  fibers,  the  latter,  after  decussating,  occupying  the  posterior  part  of  the 
lateral  columns.  The  experiments  of  Marchi,  Moeli,  Lowenthal,  and  Sherrington  seem  to  have 
established  the  fact  that  about  twenty-five  per  cent,  of  the  fibers  which  were  formerly  believed 
to  decussate  in  the  medulla  to  form  a  part  of  the  crossed  pyramidal  tract  do  not,  but  trend  back- 
ward to  pass  downward  in  the  posterior  part  of  the  lateral  columns  of  the  same  side  and  termi- 
nate about  the  nerve-cells  of  the  anterior  cornu  of  that  side.  This  view  is  supported  clinically 
by  the  fact  that  in  many  hemiplegias  there  is  also  present  a  paresis  of  the  side  of  the  lesion 
involving  particularly  the  lower  extremity. 

t  According  to  Tooth,  the  fibers  of  the  direct  cerebellar  tracts  come  directly  from  the 
posterior  nerve-roots. 


96  CKNTRAI,  NERVOUS  SYSTEM. 

where  they  bifurcate,  tlie  loni;  l)ranches  passing  upward,  the 
shon  branches  clown wartl.      (See  h'ior.  ^q.) 

The  lono-  branches  continue  upward  and  pass  by  way  of  the 
restiforni  body  to  end  about  the  cells  in  the  cortex  of  the  superior 
vermis  of  the  cerebellum  of  the  same  and  opposite  sides/='  No 
collaterals  from  the  axones  of  the  central  portion  of  this  tract  have 
been  discovered.  No  axones  from  the  cells  of  Clarke's  column 
pass  into  the  i)osterior  columns.  The  peripheral  portion  of  this 
tract  consists  of  fibers  and  collaterals  from  the  posterior  nerve- 
roots  of  the  same  side  which  pass  through  the  white  matter  of 
the  postero-external  column  and  then  enter  the  base  of  the 
posterior  horn  to  end  in  brush-like  expansions  about  the  cells 
of  Clarke  and  Stilling.  These  fibers  probably  serve  to  conduct 
sensations  of  ecjuilibrium  to  the  cells  of  Clarke  and  Stilling, 
whence  they  are  further  conveyed  via  the  direct  cerebellar  tract 
to  the  cerebellum. 

The  direct  cerebellar  tract  receives  its  myelin  at  the  seventh 
month  of  fetal  life.  P^xperimental  division  of  the  cord  in  the 
lower  animals  has  shown  that  the  long  branches  of  the  axones 
of  this  tract  degenerate  in  an  ascending  or  centripetal  direction, 
which  degeneration  ends  in  the  worm  of  the  cerebellum.  The 
short  branches  of  the  axones  of  this  tract  de<renerate  downward 
for  a  short  distance.  Their  function  is  unknown.  The  trophic 
influence  of  the  central  portion  of  this  tract  comes  from  the  cells 
of  Clarke  and  Stilling.  The  peripheral  portion  as  well,  according 
to  Edinger,  receives  its  trophic  influence  from  the  same  source. 

This  statement  of  Kdinger  is  merely  hypothetic.  It  is  more 
probable  that  the  peripheral  portion  of  this  tract  consists  of 
collaterals  from  the  posterior  nerve-roots,  which  roots  consist  of 
the  central  axones  of  the  cells  of  the  posterior  spinal  ganglia. 


♦According  to  Alexander  Bruce,  the;direct  cerebellar  tract,  after  entering  the  middle  portion  of 
the  restiform  body,  ascends  in  front  of  the  nucleus  dentatusof  the  cerebellum,  at  the  upper  mar- 
gin of  which  it  passes  backward  along  the  convex  margin  of  the  superior  cerebellar  peduncle, 
immediately  after  that  structure  has  emerged  from  the  hilum  of  the  dentate  nucleus.  At  the 
posterior  margin  of  the  peduncle  the  direct  cerebellar  tract  Ijends  inward  toward  the  superior 
worm,  terminating  on  both  sides  of  the  central,  monticulate,  and  lingual  lobules.  A  majority 
of  the  fibers  terminate  in  the  same  side  of  these  lobules,  but  a  considerable  numljer  cross  over 
to  the  same-named  lobules  of  the  opposite  side  via  the  ventral  cerebellar  commissure  of 
Stilling. 


SPINAL  CORD. 


97 


THE  COURSE  OF  THE  FIBERS  OF  THE    DORSAL    FUNICULI  OR 
POSTERIOR  COLUMNS. 

As  before  mentioned,  the  posterior  columns  are  separated  into 
two  divisions  :  an  inner  portion,  or  column  of  Goll,  or  funic- 
ulus gracilis ;  'and  an  outer  one,  the  column  of  Burdach,  wedge- 
shaped  column,  posterior  root  zone,  or  the  funiculus  cuneatus. 
Throughout  the  cervical  and  part  of  the  dorsal  regions   these 


|?'P;-^TV\::'C/ 


n 

ft 


Fig.  50. — Posterior  Cornu  and  Column  at  the  Last  Dorsal  Segment. — [After  Gowers.) 
p.  M.  C.  Posteromedian  column,  p.  E.  c.  Postero-external  column.  P.  M.  S.  Posterior  median 
septum,  p.  C.  Posterior  commissure,  v.  Commissure  vein.  P.  V.  C.  Posterior  vesicular 
column.  C.  C.  Caput  cornu.  P.  R.  Posterior  root.  a.  An  artery,  d,  d,  d.  Adjacent  to  a 
strip  of  the  lateral  column,  indicate  the  tracts  of  fibers  passing  from  the  vicinity  and  interior 
of  the  posterior  vesicular  column  along  the  septa  of  the  lateral  column,  to  form  the  direct 
cerebellar  tract,  x,  x.  Tracts  of  fibers  passing  from  the  neck  of  the  horn,  near  the  poste- 
rior vesicular  column,  to  the  postmedian  column. 

columns  are  separated  by  the  postero-intermediate  septum. 
That  these  columns  are  distinct  from  each  other  and  contain 
separate  systems  of  fibers  seems  proved  by  two  facts  :  first, 
that  the  separate  systems  of  fibers  receive  their  myelin  at  differ- 
ent periods  of  embryonic  life  ;  secondly,  from  the  study  of  the 
pathologic  appearances  of  secondary  degenerations  in  this  area. 
In  the  lumbar  and  sacral  regions  it  is  not  possible  to  separate 
the  component  fibers  of  the  posterior  columns  into  a  postero- 
7  ' 


98 


CENTRA!.  NERVOUS  SYSTEM. 


internal,  or  column  of  Goll,  and  a  posteroexternal,  or  column  ot 
Burdach.  This  is  owing  to  two  facts  :  first,  the  long  fibers 
which  arise  from  the  lower  spinal  ganglia  have  not  reached  the 
position  which  they  occupy  in  the  dorsal  region  adjacent  to  the 
posteromedian  septum  ;  second,  a  number  of  short  and  long 
fibers  exist  in  both  regions  which  do  not  take  their  origin  from 
the  spinal  ganglia,  but  originate  from  the  intrinsic  cells  of  the 
grav  matter  of  the  cord. 


EiG.  51. — Longitudinal  Skction  ok 
THE  Cord  in  the  Cervical  Re- 
gion OF  A  Sheep's  Embryo,  22 
cm.  long.  Showing  the  division  of 
the  posterior  nerve-fibers  after  enter- 
ing the  cord. —  (Laiiiiois  and  Stir- 
ling.') 


Fig.  52. — Lateral  Column  of  a  Nkw-horn 
Kahkit. 

c.  Collateral  fibers,  el.  Trending  rounding  of  the 
longitudinal  fibers  to  end  in  the  gray  matter. 
//.  Axis-cylinder  process  of  a  nerve-ceil  bend- 
ing in  among  the  longitudinal  fibers  of  the 
white  column.  /,  /,  /.  Longitudinal  fil>ers  of 
different  lengths. 


With  the  exception  of  fibers  which  come  from  the  intrinsic 
cells  at  the  base  of  the  posterior  horns, — which  form  in  the  lumbar 
and  sacral  regions  two  distinct  tracts,  the  cornu  commissural 
and  septomarginal, — the  fibers  of  which  these  columns  are  com- 
posed are  derived  from  the  posterior  nerve-roots,  which  repre- 
sent the  central  neuraxones  of  the  cells  of  the  posterior  spinal 
o-an<j"lia.  The  posterior  nerve-roots  enter  the  posterior  columns 
just  outside  of  the  posterior  horns,  in   the  region  of  the  sub- 


SPINAL  CORD.  99 

stantia  gelatinosa  Rolandi,  where  they  bifurcate,  both  divisions 
having"  a  vertical  course,  one  upward,  the  other  downward. 
Both  give  off  collaterals  nearly  at  right  angles,  which  enter  the 
gray  matter  and  break  up  into  fine  filaments  about  the  intrinsic 
nerve-cells,  or  the  motor  cells  of  the  anterior  cornua. 

The  branches  which  continue  downward  after  pursuing  a 
short  course  enter  the  gray  matter  in  curves  and  end  about 
the  nerve-cells  of  the  posterior  horns.  The  branches  which 
continue  upward  may  be  divided  into  those  having  a  short  and 
those  having  a  long  course.  The  former  pass  upward  a  variable 
distance,  and  finally  pass  into  the  posterior  horns,  to  end  about 
the  cells  in  the  gray  matter.  Those  of  long  course  pass  upward, 
and  when  they  reach  the  medulla  they  curve  slightly  forward 
and  end  in  free  arborizations  about  the  cells  of  the  nucleus 
cuneatus,  or  nucleus  of  the  column  of  Burdach,  and  nucleus 
gracilis,  or  nucleus  of  the  column  of  Goll. 

The  Column  of  Goll. — These  columns,  also  termed  the 
postero-internal  columns,  consist  of  long  fibers  only  of  the  pos- 
terior nerve-roots  from  the  various  levels  of  the  sacral,  lumbar, 
and  dorsal  regions  of  the  cord,  which  fibers  end  in  the  medulla, 
about  the  cells  of  the  nucleus  gracilis,  or  nucleus  of  the  column 
of  Goll,  of  the  same  side.  These  fibers  probably  have  the  func- 
tion of  conducting  impressions  from  the  sensory  muscle  nerves. 

The  Columns  of  Burdach. — These  columns  contain  fibers 
of  short  and  long  course,  with  their  collaterals.  The  fibers 
bifurcate,  one  division  passing  downward,  the  other  upward. 
Most  of  the  fibers  whose  course  is  downward  are  said  by  Schultze, 
Flatau,  and  Lenhossek  to  occupy  a  comma-shaped  area  in  the 
ventral  and  median  portion  of  this  column,  known  as  the  comma- 
shaped  bundle  of  Schultze.*  Hoche  has  shown  that  the  fibers  of 
the  comma-shaped  bundle  pass  in  curves  into  the  gray  matter  of 
the  cord.     In  addition,  the  median  portion  of  this  column,  in  the 

*  The  comma-shaped  bundle,  or  tract  of  Schultze,  was  formerly  believed  to  have  but  a  short 
course  and  to  consist  entirely  of  the  short  descending  axones  from  the  posterior  nerve-roots. 
Hoche  has  followed  descending  degeneration  of  this  tract  through  ten  spinal  segments,  and 
believes  the  tract  to  have  a  long  course.  Zapfer  believes  the  fibers  of  this  tract  to  come  from 
cells  in  the  gray  matter  (endogenous  fibers),  and  also  from  the  posterior  nerve-roots  (exogenous 
fibers).  Gombault,  Philipe,  and  Tooth  believe  that  this  tract  consists  of  fibers  coming  only 
from  cells  of  the  dorsal  part  of  the  gray  matter. 


lOo  CENTRAL   NERVOUS  SYSTEM. 

cervical  region  contains  long  branches,  which  pass  upward  and 
end  in  arborizations  about  the  cells  of  the  nucleus  of  the  column 
of  Burdach.  The  posterior  portion  of  this  column,  or  posterior 
root  zone,  which  borders  on  the  posterior  horn,  contains  fibers 
with  collaterals  from  the  posterior  roots,  which,  after  a  short 
course,  enter  the  posterior  horns.  Many  fibers  from  the  column 
of  Burdach  pass  into  the  column  of  Goll,  as  is  shown  by  the 
study  of  secondary  degeneration.* 

The  majority  of  the  fibers  from  both  of  these  columns  depend 
for  their  nutrition  upon  the  cells  of  the  posterior  spinal  ganglia. 
The  fibers  degenerate  in  the  direction  in  which  they  pass.  The 
fibers  which  degenerate  downward  occupy  three  areas :  first,  the 
comma-shaped  area  in  Burdach's  column  ;  second,  the  area  of 
the  septomarginal  tract ;  and  third,  the  area  of  the  cornu  com- 
missural tract.  A  complete  transverse  section  of  the  nerves 
composing  the  cauda  equina  results  in  a  complete  degeneration 
of  the  root-fibers  that  enter  into  the  formation  of  the  posterior 
columns  at  the  point  where  the  cauda  equina  merges  into  the 
cord.  Just  above  this  area  where  new  fibers  enter,  the  degen- 
erated area  now  occupies  the  entire  column  of  Goll,  with  a 
portion  only  of  Burdach's  column.  Higher  up  the  cord  this 
degenerated  area  is  confined  to  the  column  of  Goll,  and  passes 
upward  to  terminate  about  the  cells  of  the  nucleus  of  that  column 
in  the  medulla. 


THE  CORNU  COMMISSURAL  AND  SEPTOMARGINAL  DESCENDLNG 

TRACTS. 

That  the  fibers  of  which  both  of  these  tracts  are  composed 
have  their  origin  from  the  intrinsic  cells  of  the  posterior  part  of 
the  gray  matter  of  the  cord  seems  proved  from  the  fact  that 
they  are  not  found  degenerated  when  the  posterior  nerve-roots 


*  Flechsig  and  Bechterew,  on  embryologic  grounds,  have  divided  the  fibers  of  vehich  the 
columns  of  Burdach  are  composed  into  three  root  zones— an  anterior,  a  middle,  and  a  posterior. 
The  anterior  root  zone  lies  between  the  posterior  commissure,  base  of  posterior  horn,  and 
posterior  median  fissure.  The  middle  root  zone  lies  between  the  anterior  and  posterior  root 
zones,  being  bounded  on  the  inner  side  by  Goll's  column,  and  on  the  outer  side  by  the  posterior 
horn.  The  posterior  root  zone  occupies  the  dorsal  part  of  Burdach's  column,  and  rests  a^rain>t 
the  dorsal  periphery  of  the  cord. 


SPINAL  CORD.  loi 

are  experimentally  divided,  or  when  they  are  atrophied,  the 
result  of  disease.  In  locomotor  ataxia,  a  disease  which  is  now 
universally  regarded  as  due  to  sclerosis  of  the  posterior  nerve- 
roots,  the  fibers  of  these  two  tracts  remain  undegenerated,  and 
are  in  striking  contrast  to  the  degenerated  fibers  in  the  pos- 
terior column  from  the  posterior  nerve-roots.  The  fibers  of 
these  two  fasciculi  degenerate  downward  when  the  diseased 
process  destroys  the  intrinsic  cells  existing  in  the  posterior  part 
of  the  gray  matter  of  the  cord,  such  degeneration  having  been 
observed  by  Hoche  in  two  cases  of  compression  myelitis.  Other 
observers   have   found   them   degenerated   in   cases  of  syringo- 


S,.M. 


Fig.  53. — Transverse  Section  op'  the  Spinal  Cord  at  the  Level  of  the  First 

Sacral  Segment. — [After  Alexander  Bruce.) 

S.  M.   Septomarginal  tract.      C.  C.   Cornu  commissural  tract. 

myelia,  which  is  a  gliosis  affecting  at  first  the  gray  matter  sur- 
rounding the  central  canal  and  then  gradually  extending  in  all 
directions  from  that  point  (Fig.  53). 

The  Cornu  Commissural  Tract. — This  tract  lies  in  the 
anterior  part  of  the  posterior  column,  adjacent  to  the  posterior 
commissure,  posterior  cornu,  and  the  posterior  median  septum. 
It  attains  its  greatest  size  in  the  lower  lumbar  region,  and  dimin- 
ishes in  size  both  above  and  below  this  level.  This  tract  extends 
throughout  the  lumbar  and  sacral  regions  of  the  cord,  originating 
as  high  as  the  eleventh  dorsal  segment  and  terminating  at  the 
fifth  sacral  segment. 


I02  fKNTRAl.    NERVOLS  SYSTEM. 

The  Septomarginal  Tract. — This  tract,  as  its  name  denotes, 
is  locatcil  along  the  margin  of  the  posterior  median  septum.  It 
attains  its  greatest  size  in  the  sacral  and  lumbar  regions.  It 
consists  of  a  narrow  strip  of  fibers  located  alongside  the  median 
septum,  extending  in  the  sacral  region  as  far  forward  as  the 
cornu  commissural  tract,  with  which  its  fibers  commingle,  and 
reaching  backward  to  the  periphery  of  the  cord,  where  it  expands 
into  an  oval-shaped  area.  At  the  level  of  the  fifth  lumbar  seg- 
ment this  tract  is  much  reduced  in  size,  extending  ventrallv  to 
about  one-half  the  length  of  the  septum,  and  being  entirely 
distinct  from  the  cornu  commissural  tract.  Above  this  level  it 
rapidly  diminishes  in  size,  until  at  the  level  of  the  third  lumbar 
segment  it  occupies  a  slight  triangular  field  bordering  on  the 
posterior  part  of  the  septum  and  the  adjoining  part  of  the  per- 
iphery of  the  cord.  At  the  level  of  the  twelfth  dorsal  segmeot 
it  is  entirely  displaced  from  its  position  along  the  septum,  and 
comes  to  occupy  a  small  area  along  the  dorsolateral  periphery 
of  the  posterior  column.  Hoche  has  proved  that  this  tract  may 
oriofinate  as  h'lQ-h  as  the  lowest  cervical  seofment,  and  that  its 
fibers  continue  downward  into  the  filum  terminale. 

In  the  cervical  region,  owing  to  the  fact  that  the  nerves 
coming  from  the  lower  extremity  occupy  the  column  of  Goll 
and  those  of  the  upper  extremity  are  confined  to  Burdach's 
column,  a  section  of  the  cervical  nerves  at  this  level  produces 
an  ascending  degeneration,  confined  to  Burdach's  column,  which 
degeneration  passes  upward,  terminating  about  the  cells  of  the 
nucleus  of  this  column  in  the  medulla.  Thus,  the  study  of  sec- 
ondary degeneration  proves  that  the  entering  posterior  nerve- 
roots  are  located  close  to  the  posterior  horns,  and  that  the  fibers 
which  enter  the  cord  at  higher  levels  displace  inward,  toward 
the  column  of  Goll,  those  that  have  entered  below,  so  that  in 
the  cervical  region  the  fibers  from  the  lower  extremities  occupy 
almost  entirely  the  columns  of  Goll,  while  most  of  those  from 
the  arms  are  located  in  the  columns  of  Burdach. 


SPINAL  CORD. 


103 


GOWERS'    ANTEROLATERAL   ASCENDING    TRACT— FASCICULUS 
VENTROLATERALIS    SUPERFICIALIS. 

This  tract  consists  of  neuraxones  from  the  intrinsic  cells  of 
the  intermediate  gray  matter,  and  from  cells  at  the  base  of  the 
anterior  horns.  This  origin  has  been  positively  proved  by  the 
experiments  of  Mott,  who  found  that  when  the  posterior  nerve- 
roots  only  were  severed  Gowers'  tract  remained  undegene- 
rated,  but,  on  the  other  hand,  when  the  intermediate  gray  matter 
was  injured  or  destroyed,  this  tract  was  found  degenerated 
throughout  its  entire  extent.     The  axones  from  these  intrinsic 


Fig.  54. — Course  and  Termination  oe  Gowers'  Tract. — [Aa-ording  to  Hoche. 


cells  doubtless  decussate  in  the  anterior  commissure  of  the  cord, 
and  pass  obliquely  across  the  white  matter  of  the  anterolateral 
area  of  the  cord,  where  they  occupy  a  broadly  comma-shaped 
area,  situated  midway  between  the  periphery  and  gray  matter,  in 
front  of  the  direct  cerebellar  and  crossed  pyramidal  tracts,  and 
extending  as  far  forward  as  the  anterior  nerve-roots,  being  sepa- 
rated from  the  periphery  of  the  cord  by  the  anterolateral  de- 
scending tract  of  Marchi  and  Lowenthal.  This  tract  increases 
in  size  from  below  upward,  and  passes  into  the  anterolateral 
field  of  the  formatio  reticularis  of  the  medulla  oblongata,  in  which 


I04  CENTRAL   NERVOUS  SYSTEM. 

region  some  of  the  fibers  may  be  connected  witli  the  cells  of  the 
lateral  nucleus.  This  bundle  then  continues  onward  through 
the  medulla  and  pons  as  far  as  the  root  of  the  trigeminal  nerve, 
beyond  which  point  its  course  is  in  much  dispute.  According 
to  Hoche,'^'  the  terminal  course  of  Gowers'  tract  is  as  follows  : 
At  the  level  of  the  upper  half  of  the  olivary  body  the  direct 
cerebellar  tract  turns  backward  into  the  restiform  body,  while 
Gowers'  tract  continues  upward  through  the  medulla  and  pons 
to  the  region  of  the  trioeminal  or  fifth  nerve,  around  which  nerve 
it  curves,  and  passes  into  the  cerebellum  by  means  of  the  velum 
medullare  anticum  and  superior  cerebellar  peduncle. 

Mott,  however,  after  studying  the  course  of  Gowers'  tract  in 
monkeys,  believes  it  to  consist  of  two  afferent  bundles — axones 
from  the  gray  matter  of  the  cord  :  one,  the  ventral  cerebellar 
tract,  occupying  the  most  peripheral  part  of  this  area,  which,  on 
reaching  the  pons,  forms  a  loop  over  the  fifth  nerve  to  join  the 
superior  cerebellar  peduncle,  and  then  descends  on  its  posterior 
aspect  to  the  middle  lobe  or  vermis  of  the  cerebellum.  The 
remaining  bundle,  which  he  terms  the  crossed  afferent  tract  of 
Gowers  and  Edinger,  continues  upward  through  the  cord,  the 
medulla,  and  the  pons,  beyond  which  it  lies  outside  of  the  lateral 
fillet  or  lemniscus,  and  terminates  in  the  corpora  quadrigemina, 
some  fibers  continuing  to  the  optic  thalamus. 

Bechterew  has  shown  that  the  constituent  fibers  of  this  tract 
receive  their  myelin  at  the  eighth  fetal  month. 

The  function  of  this  tract,  according  to  Gowers,  is  to  conduct 
sensations  of  pain  and  temperature,  and  the  very  interesting 
case  recently  reported  by  Henry  Hun  is  confirmatory  of  the 
same  fact.t 


THE  ANTEROLATERAL  DESCENDING    CEREBELLAR  TRACT    OF 
MARCHI  AND   LOWENTHAL. 

This  tract  of  fibers,  discovered  by  Lowenthal,  is  located  ventrad 

*  Hoche's  case  is  the  only  one  in  man  in  which  Gowers'  tract  has  been  completely  traced. 
See  original  article  in  "  Archives  fiir  Psychiatrie  unci  Nervenkrankheiten,"  1896,  p.  510. 

t  "New  York   Medical  Journal ""    for  April  17,  May  I  and  8,  1897':     'Analgesia,  Thermic 
Anesthesia    and  Ataxia." 


SPINAL  CORD.  105 

to  the  crossed  pyramidal  tract,  and  extends  along  the  antero- 
lateral periphery  of  the  cord  as  far  forward  as  the  anterior 
median  fissure,  some  of  its  fibers  being  commingled  with  those 
of  Gowers'  tract.  That  this  tract  is  distinct  from  the  motor 
tracts  seems  proved  by  the  fact  that  it  has  never  been  found 
degenerated  after  disease  or  ablation  of  the  motor  area  of  the 
brain.  While  the  exact  position  of  the  anterolateral  descending 
tract  in  the  cord  is  well  known,  the  source  and  distribution  of 
its  component  fibers  still  remains  in  much  doubt.  The  experi- 
ments of  Marchi  and  Biedl  seem  to  prove  that  the  fibers  of  this 
tract  have  their  origin  in  the  cerebellum.  Marchi  found  that, 
after  hemi-extirpation  of  the  cerebellum,  a  secondary  descend- 
ing degeneration  occurred  in  the  spinal  cord,  the  degenerated 
area  corresponding  exactly  to  the  known  anatomic  position  ot 
this  tract.  Biedl  also  found,  on  experimental  division  of  the 
restiform  body,  a  similar  degeneration,  thus  confirming  the 
earlier  experiments  of  Marchi.  Ferrier,  Turner,  and  Risien 
Russel,  on  the  contrary,  found  the  anterolateral  descending 
tract  degenerated  after  destruction  of  Deiter's  nucleus,  the 
cerebellum  and  restiform  body  being  intact.  According  to 
Risien  Russel.  this  tract  of  fibers  occupies  a  position  in  the  for- 
matio  reticularis  between  the  descending  root  of  the  fifth  nerve 
and  the  raphe ;  the  fibers  pass  downward  between  the  inferior 
olivary  body  and  the  lateral  nucleus,  occupying  the  anterolateral 
periphery  of  the  cord  as  far  forward  as  the  anterior  median 
fissure.  The  anterolateral  descending  tract  extends  through- 
out the  cord,  but  decreases  in  size  from  above  downward.  The 
fibers  of  which  it  is  composed  may  enter  the  anterior  horns  at 
different  levels,  to  terminate  about  their  nerve-cells. 


THE  OLIVARY  TRACT  OF  BECHTEREW. 

The  olivary  fasciculus,  or  the  triangular  bundle  of  Helweg, 
appears  on  transverse  section  as  a  small  triangular  area  of 
fibers  located  in  the  ventral  part  of  the  anterolateral  portion 
of  the  spinal  cord,  with  its  base  resting  against  the  periphery  of 
the  cord.  The  most  lateral  fibers  of  the  anterior  nerve-roots 
frequently  pass  through  this  triangular  area.     At  the  beginning 


io6  CENTRAL   NKRVOLS  SYSTEM. 

of  the  motor  decussation  the  olivar\'  tract  becomes  spread  out 
and  loses  its  triangular  shape.  Just  above  the  motor  crossway 
the  fibers  of  this  tract  occupy  an  oblong  field  along  the-  ventral 
periphery  of  the  medulla,  adjacent  to  the  anterior  pyramid.  At 
the  beg'inning  of  the  inferior  olivary  body  the  tract  becomes 
much  reduced  in  size,  and  again  assumes  a  triangular  form,  the 
base  of  which  caps  the  inferior  part  of  the  olive.  At  a  higher 
level  the  tract  appears  to  have  joined  the  olivary  body.  It  is 
possible,  as  suggested  by  Bechterew,  that  the  fibers  of  which 
this  tract  is  composed  are  axones  from  cells  of  the  olivary  body. 
The  fibers  of  this  tract,  according  to  Bechterew,  become  medul- 
lated  after  birth,  hence  they  are  entirely  distinct  from  the  motor 
tracts  or  from  the  ground  bundles  of  fibers.  Because  the  fibers 
of  the  olivary  tract  become  medullated  at  about  the  same  time 
as  those  of  the  central  tegmental  tract  of  the  medulla,  Bechterew 
believes  that  both  tracts  form  a  functionally  continuous  system 
of  fibers. 


A  LONG  SENSORY  TRACT  IN  THE  GRAY  MATTER  (CIAGLINSKI ). 

In  connection  with  the  sensory  tracts  of  the  cord,  mention  may 
be  made  of  a  long  sensory  tract  of  fibers  in  the  gray  matter  of  the 
cord,  discovered  in  1896  by  Adam  Ciaglinski.  This  tract  of  fibers 
is  somewhat  pyramidal  in  shape  on  transverse  section,  and  is 
located,  according  to  Ciaglinski,  in  the  gray  commissure  between 
the  ventral  border  of  the  posterior  columns  and  the  central  canal. 
It  has  been  traced  from  the  lumbar  cord  to  the  cervical  enlarge- 
ment. Ciaglinski  believes  its  fibers  to  come  from  the  posterior 
nerve-roots,  and  thinks  that  it  may  conduct  sensatrons  of  pain 
and  temperature.  Further  clinical  and  experimental  evidence 
must  be  at  hand  before  any  positive  statements  regarding-  this 
tract  can  be  made. 


LISSAUER'S  TRACT. 

This  comprises  an  area  which  surrounds  the  tip  ot  the  posterior 
horns,  extending  in  part  into  the  lateral  column  and  in  part  into 
the   column  of  Burdach.     It  is  composed  more  particularly  of 


SPINAL  CORD.  107 

fibers  from  the  lateral  division  of  the  posterior  nerve-roots. 
These  fibers  soon  divide,  passing  up  and  down  and  giving  off 
collaterals,  which,  with  the  axones,  enter  the  posterior  horns  and 
finally  terminate  in  brush-like  expansions  about  the  cells  existing 
in  those  horns. 


ANTERIOR  GROUxND  BUNDLES. 

The  anterior  ground  bundles  occupy  all  of  the  anterior 
columns  of  each  side  save  the  direct  pyramidal  tract,  the  fibers 
of  Gowers'  tract,  and  those  of  Marchi  and  Lo  wen  thai.  They 
are  collections  of  fibers  which  extend  throughout  the  entire 
length  of  the  cord,  and  consist  of  neuraxones  from  the  intrinsic 
cells  of  the  gray  matter  which  lie  near  the  base  of  the  anterior 
horns.  These  neuraxones  mosdy  cross  in  the  anterior  white 
commissure,  although  some  fibers  of  the  same  side  enter  the 
anterior  ground  bundle  of  that  side.  After  entering  these 
columns  the  axones  branch  T-shaped,  one  branch  passing  upward, 
the  other  downward,  both  branches  having  only  a  short  course. 
They  give  off  collaterals  at  right  angles.  The  branches,  with 
their  collaterals,  reenter  the  gray  matter  at  higher  and  lower 
levels,  and  end  in  brush-like  expansions  among  the  motor  and 
intrinsic  cells  of  the  anterior  cornua. 

At  the  point  of  the  motor  crossing  in  the  medulla,  part  of  the 
fibers  of  the  ground  bundles  are  pressed  backward  into  the 
posterior  part  of  the  formatio  reticularis,  where  they  continue 
upward  as  a  distinct  bundle  of  nerve-fibers  on  each  side  of  the 
raphe,  and  from  this  point  on  are  called  the  posterior  longitudinal 
bundles. 

One  of  the  functions  of  this  system  of  fibers  is  to  associate 
different  levels  of  the  anterior  cornua,  thus  bringing  into  harmony 
the  action  of  the  motor-cells  of  various  levels. 


THE  GROUND  BUNDLES  OF  THE  LATERAL  COLUMNS,  OR  THE 
LATERAL    LIMITING    LAYERS. 

These   bundles  of  fibers  occupy  areas  adjacent  to  the  gray 
matter  of  the  cord  between  the  anterior  nerve-roots  and  base  of 


lo8  CLMRAI.   NKRVOUS  SYSTEM. 

the  posterior  horns  of  each  side.  They  are  composed  of  neur- 
axones  from  the  intrinsic  cells  of  the  intermediate  gray  matter 
of  the  same  and  opposite  sides.  The  axones  pass  into  the  white 
matter  and  bifurcate,  passing,  after  a  short  course,  upward  and 
downward;  with  their  collaterals,  reenter  the  gray  matter  at 
higher  and  lower  levels,  where  the)-  divide  into  fine  filaments 
about  the  intrinsic  nerve-cells.  These  bundles  are  traversed  by 
many  fibers  from  the  cells  of  the  gray  matter  passing  across  the 
lateral  columns,  and  also  by  fibers  entering  the  gray  matter 
from  the  crossed  pyramidal  tract.  They  may  serve  to  associate 
different  levels  of  the  gray  matter.  Experimental  evidence 
seem.s  to  prove  that  the  fibers  of  the  ventral  portion  of  the 
lateral  limiting  layer  associate  different  levels  of  the  anterior 
cornu  of  the  same  side,  while  the  fibers  of  the  dorsal  portion 
probably  associate  difierent  levels  of  the  posterior  cornu  of  the 
same  side. 


THE  SPINAL  NERVES. 

There  are  thirty-three  pairs  of  spinal  nerves  in  man,  each 
pair  corresponding  to  a  spinal  segment.'-'  According  to  the  region 
from  which  they  issue,  they  are  termed  cervical,  dorsal,  lumbar, 
sacral,  and  coccygeal  nerves,  there  being  eight  cervical,  twelve 
dorsal,  five  lumbar,  five  sacral,  and  three  coccygeal  nerves. 
These  nerves — each  possessing  an  anterior  and  a  posterior  root 
— emerge  from  the  cord  at  regular  intervals.  The  anterior  roots, 
which  leave  the  cord,  arise  from  the  multipolar  cells  of  the  ante- 
rior horns  and  pass  out  through  the  anterolateral  columns  of 
the  cord.  The  posterior  roots,  which  enter  the  cord,  have  their 
point  of  entrance *at  the  posterolateral  sulci. 

These  nerve-roots  are  made  up  of  filaments, — from  five  to  ten 
in  number  for  each  root, — the  posterior  roots  having  their  fila- 
ments associated  into  two  bundles.  The  posterior  sensory  roots 
are  of  greater  size  than  the  anterior  or  motor  roots,  and  have 
connected  with  them  the  posterior  spinal  ganglia. 

*  Most  anatomists  only  enumerate  thirty-one  pairs  of  spina!  nerves;  this  is  owing  to  the  fact 
that  the  two  lowest  pairs  of  coccygeal  nerves  are  rudimentary,  and  hence  without  special 
function. 


SPINAL  CORD. 


109 


SPINAL  GANGLIA. 

The  spinal  ganglia  are  in  general  located  in  the  epidural  space, 
just  in  front  of  or  within  the  intervertebral  foramina.  The  ganglia 
connected  with  the  sacral  nerves,  however,  are  contained  within 
the  subdural  space  of  the  spinal  canal.  The  spinal  ganglia  are 
oval,  usually  bilobate,  the  lobes  corresponding  to  the  two  bundles 
of  filaments  into  which  each  sensory  nerve-root  is  divided.  Each 
ganglia  is  made  up  of  a  large  number  of  cells,  chiefly  unipolar, 
spheric,  or  slightly  pyriform  in  shape,  and  between  60  to  80  f.i 


-f- 


^^-^ 


Fig.  55. Transverse  Section  through  a  Posterior  Spinal  Ganglion.     Stained  after 

the  method  of  Weigert. 


in  diameter  ;  great  variations  in  size  occur,  the  largest  being  as 
much  as  170  i^i  in  diameter,  and  the  smallest  as  low  as  25  ^^  in 
diameter  (Figs.  55  and  56). 

Each  cell  is  surrounded  by  a  distinct  connective-tissue  capsule, 
which  is  continuous  with  Henle's  sheath  of  the  corresponding 
axis-cylinder,  and  is  lined  with  a  layer  of  epithelium.  Beneath 
this  capsule,  surrounding  the  protoplasm  of  the  cell,  exists  a 
small,  clear,  homogeneous,  unstainable  space  devoid  of  granules. 
This   seems  to  indicate  that  the  protoplasm  does  not  entirely 


CENTRAL    NKRVOLS  SVSTKM. 


occupy  the  capsule  ;  at  least  Lenhossek  says  that  this  clear  space 
is  not  an  artifact,  tlue  to  the  shrinking-  of  the  protoplasm  during- 
the  process  of  hardening.  The  protoplasm  is  made  up  chiefly 
of  chromophyllic  granules.  These  granules  are  ver}'  fine 
throughout  the  body  of  the  cell,  but  around  the  periphery  there 
exists  a  layer  of  much  coarser  granules.  The  construction  of 
the  matrix  in  which  these  granules  are  embedded  is  still  in 
dispute.      By  some  it  is  considered  to  be  composed  of  a  number 


Fig.  56. — A   Group  ok   Cki.ls   krom  a   Human  Posterior  Simnal  Ganglion.     Stained 

after  the  method  of  Nissl. 


of  fine  fibrillae,  continuous  with  the  fibrillse  composing  the 
axones,  while  others  assert  that  no  such  fibrillae  exist.  These 
latter  believe  that  the  matrix  is  simply  a  homogeneous  ground 
substance  in  which  the  granules  are  embedded.  Most  of  the 
cells  of  the  posterior  spinal  ganglia  are  very  deeply  pigmented, 
the  pigmentation  being  limited  to  the  protoplasm,  and  occurs 
most  often  near  the  point  of  exit  of  the  axone. 

These  cells  contain   a  large  spheric   nucleus,  surrounded  by 


SPINAL  CORD.  Ill 

a  distant  nuclear  membrane.  It  is  centrally  located,  contains  a 
small  nucleolus,  and  is  made  up  of  very  fine  granules.  By  far 
the  greater  number  of  these  cells  are  monopolar,  and  hence 
oive  off  but  one  axone.  This  axone,  at  a  short  distance 
from  the  cell-body,  bifurcates  T-shaped,  one  branch  passing 
peripherally  to   terminate   in   a   sensory   end  organ,   while  the 


)\^_^^  ■"'"■  B 

Fig.  57. — Schematic   Representation   to  show  the  Origin  and   Relations  of  the 

Anterior  and  Posterior  Spinal  Nerve-roots. 

A.   Anterior  or  motor  nerve-roots.      B.   Posterior  or  sensory  nerve-roots.      D.    Posterior  spinal 

ganglia.      F.    Central,  E,  peripheral,  axones  of  the  posterior  spinal  ganglia. 


Other  continues   centrally  to  arborize  about  nerve-cells  in  the 
spinal  cord  or  medulla  oblongata. 

A  few  of  these  cells  are  bipolar,  giving  off  two  axones,  one 
from  each  pole,  one  of  which  is  peripheral  as  above  and  the 
other  central.  According  to  Dogiel,  there  exists  in  the  posterior 
spinal  ganglia  numerous  small  cells  which  he  calls  spinal  ganglion 
cells  of  the  second  type.  These  cells  might  be  very  properly 
termed  the  intrinsic  cells  of  the  posterior  spinal  ganglia.     The 


112  CENTRAL  NERVOUS  SYSTEM. 

chief  axone  of  each  cell  terminates,  after  losing  its  myelin  sheath, 
in  an  arborization  about  and  within  the  capsule  of  a  chief  s[)inal 
ganglion  cell,  forming  an  extra-  and  intra-capsular  network. 
Dogiel  further  asserts  that  these  intrinsic  cells  are  in  turn  sur- 
rounded by  the  termination  of  sympathetic  nerve-fibers. 

The  function  of  these  posterior  spinal  ganglia  is  doubtless 
trophic,  since  on  section  of  the  nerve-roots  posterior  to  their 
ganglia  the  fibers  degenerate  to  their  peripheral  destination, 
while  if  they  are  divided  anterior  to  their  ganglia,  there  is  an 
ascending  degeneration  of  the  fibers  which  continues  as  far 
as  they  extend,  the  short  fibers  to  the  posterior  horns,  the  long- 
fibers  to  their  nuclei  in  the  medulla.  According  to  Edinger, 
the  sensory  fibers,  carrying  impressions  of  equilibrium  to  the 
cells  of  Clarke  and  Stilling,  are  dependent  on  these  cells  for 
their  nutrition  and  not  upon  the  cells  of  the  spinal  ganglion, 
merely  passing  between  them  in  their  course.  The  anterior  and 
posterior  nerve-roots  become  continuous  in  the  intervertebral 
foramina,  and  continue  peripherally  as  mixed  nerves,  having 
both  motor  and  sensory  functions.     (See  Fig.  57.) 


THE  ANTERIOR  OR  MOTOR  NERVE-ROOTS. 

The  anterior  nerve-roots,  which  consist  of  both  coarse  and  fine 
fibers  and  are  distributed  to  the  voluntary  muscles,'^'  are  the 
neuraxones  of  the  motor  cells  of  the  anterior  cornua  of  the 
spinal  cord.  The  multipolar  cells  of  large  size  give  off  axones 
which  are  greater  in  diameter  than  are  those  from  the  multi- 
polar cells  of  smaller  size.  There  are  three  distinct  bundles  of 
these  axones,  which  form  the  anterior  nerve-roots  :  first,  a  lateral 
bundle,  coming  from  the  lateral  cell  group  ;  second,  a  median 
bundle,  arising  from  the  median  cell  group  ;  and  lastly,  an  inner 
bundle,  springing  from  the  anterior  cell  group. 

These  axones  give  off  a  few  collaterals,  the  termination  of 
which  remains  unknown.  The  anterior  nerve-roots  pass  out  of 
the  anterolateral  area  of  the  cord  in  curves,  and  take  mostly  a 


*  According  to  Gaskell  and  Mott,  the  fine  fibers  join  the  sympathetic  system  and  are  distributed 

to  the  involuntary  muscles  of  the  internal  organs. 


SPINAL  CORD.  113 

downward  direction.  The  curvature  of  the  anterior  nerve-roots 
gradually  increases  from  above  downward,  so  that  while  in  the 
cervical  region  they  are  given  off  almost  at  right  angles,  with 
exception  of  the  first  cervical  nerve,  which  ascends  slightly,  to  pass 
between  the  atlas  and  occipital  bone.     In  the  dorsal  region  they 


/* 


Fig.  58. — A  Section  through  the  Spinal  Cord  of  a  New-born  ]\Iouse.  Showing 
reflex  collaterals  from  posterior  nerve-roots  terminating  about  the  nerve-cells  of  the  anterior 
horn. — {^A/ter  Lenhossek.) 

are  oblique,  and  in  the  lumbar  and  sacral  regions  their  course  is 
almost  vertical. 


THE  POSTERIOR  OR  SENSORY  NERVE-ROOTS. 

These  roots,  on  entering  the  cord,  are  arranged  into  two 
bundles — a  lateral  and  a  mesial.  The  former  is  composed  of 
fibers  of  small  size,  which,  near  the  tip  of  the  posterior  horn, 


114  CENTRAL  NERVOUS  SYSTEM. 

enter  the  substantia  gelatinosa.  become  vertical,  and  form  the 
boundary  zone  or  cohunn  of  Lissauer.  Tlie  mesial  bundle 
consists  of  fibers,  some  of  which  pass  into  the  column  of  Hurdach, 
while  others  pass  through  that  column  into  the  column  of  Goll. 
All  these  root-fibers  bifurcate  on  entering-  the  cord,  one  process 
passing  upward,  the  other  downward.  Both  divisions  are  con- 
stantly giving  off  collaterals  at  varying  distances.  Many  of  the 
fibers  having  a  downward  course  unite  to  form  a  comma-shaped 
fasciculus  or  tract  in  the  median  portion  of  Burdach's  column. 

Those  fibers  which  pass  upward,  with  the  exception  of  those 
which  reenter  the  gray  matter  (see  posterior  column),  end 
about  the  cells  of  the  nuclei  of  the  columns  of  Burdachand  Goll 
in  the  medulla.  The  collaterals  from  these  longitudinal  fibers 
all  pass  into  the  gray  matter,  and  may,  in  general,  be  divided  into 
three  sets:  First,  collaterals  which  pass  across  the  intermediate 
gray  matter  to  end  in  brush-like  expansions  about  the  motor 
nerve-cells  of  the  same  side ;  these  are  called  sensorimotor 
or  reflex  collaterals  ;  second,  collaterals  which  end  in  arboriza- 
tions about  the  cells  of  Clarke  and  Stillinorand  the  intrinsic  cells 
of  the  gray  matter  ;  these  collaterals  come  largely  from  the 
middle  region  of  Burdach's  column ;  third,  collaterals  which 
pass  across  in  the  posterior  or  gray  commissure  and  end  among 
cells  in  the  fine  network  of  fibers  of  the  substantia  trelatinosa 
of  the  posterior  horn  of  the  opposite  side.*   (See  Figs.  45  and  59.) 


THE  APPEARANCES  OF  TRANSVERSE  SECTIONS  OF 
THE  CORD  AT  DIFFERENT  LEVELS. 

In  the  sacral  region  there  is  a  preponderance  of  gray  matter, 
there  being  only  a  thin  layer  of  white  matter,  the  most  of  which 
exists  in  the  posterior  columns.     In  general,  the  anterior  and 

*  According  to  Moral  and  Bonne,  there  are  present  in  the  posterior  nerve-roots  a  few 
centrifugal  elements.  They  proved  this  fact  by  observing  that,  on  stimulation  of  the  peripheral 
end  of  a  severed  posterior  nerve-root,  there  occurred  vasomotor  phenomena  in  the  area  of  distri- 
bution of  the  nerve.  They  also  found  that,  on  section  of  the  posterior  nerve-roots  of  the  last 
lumbar  and  first  sacral  segments  central  to  the  ganglia,  on  the  central  side  of  the  section  the 
great  majority  of  the  fibers  degenerated,  while  a  few  remained  normal.  In  the  peripheral  end, 
on  the  contrary,  most  of  the  fibers  remained  normal,  while  a  few  degenerated,  thus  proving  that 
a  few  fibers  degenerated  downward  and  receive  their  nutrition  higher  up  in  the  cord  or  in  the 
brain  stem.      These  facts  remain  to  t)e  corroborated  by  future  observations. 


SPINAL  CORD. 


"5 


posterior  horns  resemble  each  other  in  size  and  thickness.     The 

lateral  horns  are  well  marked.     The  commissure  is  very  broad. 

The  conus  termmalis  on  transection  resembles   closely  similar 

sections  of  the  lower  sacral  part  of  the  cord,  the  gray  matter 


Fig.  59. — Diagram  showing  the  Relative  Size  and   Form   of   Different  Segments 
OF  the  Coccygeal,  Sacral,  Lumbar,  Dorsal,  and  Cervical  Cord.— (^/?fr  Gowers.) 


preponderating,  while  the  white  matter  consists  of  a  very  thin 
margin,  most  evident  in  the  lateral  columns. 

In  the  lumbar  region  the  outline  of  the  cord  is  circular,  the 
anterior  horns  are  much  broader  and  thicker  than  the  posterior. 
There  exist  in  the  anterior  horns  well-defined  groups  of  motor 
nerve-cells,  which  give  exit  to  a  large  number  of  motor  nerves 


Il6 


CENTRAL  NERVOUS  SYSTEM. 


which  are  distributed  to  the  lower  extremities.  The  lateral 
horns  are  distinct  only  in  the  lower  segments.  The  white 
matter  preponderates,  owing  to  the  great  number  of  nerve- 
fibers  received  from  the  lower  extremities. 

In  the  dorsal  or  thoracic  region  the  gray  matter  consists  of 
two  narrow  crescentic  bodies  united  by  means  of  a  band  of  gray 


Fk;.    6o. — Transverse   Section   through    a   Sacral    Segment   ok   the  Sitnai.  Coru. 

Weigert  preparation. 
a.  Pia  mater.     /'.  Arachnoid,     c.   Dura  mater,     d,  d.     Severed  descending  nerve-roots,      i. 
Anterior  column.      2.   Lateral  column.     3.    Posterior  column.     4,4.  Cell  groups  of  Stilling. 

and  white  matter — the  commissures.  The  lateral  horns  are  well 
seen  only  in  the  upper  segments.  The  anterior  and  posterior 
horns  are  about  equal  in  thickness,  but  the  anterior  horn  is 
much  shorter,  and  contains,  in  this  region,  very  few  ganglionic 
cells.  In  the  upper  part,  at  the  base  of  the  posterior  horn,  is 
the  group  of  the  cells  of  Clarke.  The  great  amount  of  white 
matter  is   the   striking   feature  of  transverse    sections   of    this 


SPINAL  CORD.  '  117 

region.  In  the  upper  part  is  found  the  beginning  of  the  postero- 
intermediate  septum,  which  is  the  dividing-Hne  between  the 
columns  of  Goll  and  Burdach. 

In  the  cervical  region  there  is  a  general  increase  in  the  size 
of  the  cord,  which  affects  the  gray  as  well  as  the  white  matter. 
This  is  due  to  the  fact  that  this  reg-ion  receives  the  fibers  from 
the  upper  extremities  as  well  as  the  long  and  short  tracts  from 
below.  The  cord  is  flattened  anteroposteriorly,  hence  loses  its 
cylindric  form.  The  lateral  horns  are  very  prominent,  and  in 
the  upper  segment  exists  a  cell-group  at  the  base  of  these 
horns,  which  group  gives  origin  to  the  spinal  accessory  or 
eleventh  pair  of  cranial  nerves.  The  processus  reticularis  is 
prominent  on  the  outer  side  of  the  gray  matter  between  the 
anterior  and  posterior  horns.  The  anterior  horns  are  short  and 
broad  and  appear  of  large  size,  which  is  due  somewhat  to  the 
lateral  extension  of  gray  matter  forming  the  lateral  horns. 
The  posterior  horns  are  long  and  slender  and  gently  diverge, 
the  divergence  increasing  as  the  segments  gradually  approach 
the  medulla.  At  the  same  time  the  central  canal  trends  back- 
ward and  assumes  a  somewhat  flattened  appearance.  The 
nerve-roots  leave  the  cord  at  nearly  right  angles. 


NEUROGLIA  OF  THE   SPINAL  CORD. 

The  neuroglia  of  the  cord,  as  elsewhere  throughout  the  central 
nervous  system,  consists  of  large  numbers  of  neuroglia  cells 
(astrocytes)  with  their  processes,  which  latter  pass  between  the 
nerve-fibers  and  cells  and  around  the  blood-vessels,  forming  a 
supporting  framework,  ground  substance,  or  stroma,  in  which 
the  elements  of  the  cord  are  embedded.  In  addition  to  the 
neuroglia  cells  described  under  head  of  histologic  elements, 
there  occurs  lining  the  central  canal  of  the  cord,  as  well  as  the 
ventricles  of  the  brain,  a  supporting  framework  similar  in  func- 
tion to  neuroglia  tissue,  but  made  up  of  the  so-called  ependymal 
cells  and  processes.  In  the  cord  during  embryonic  life  these 
cells  are  oval  or  fusiform  in  shape,  and  are  arranged  around  the 
central  canal  in  a  radiating  manner.  They  possess  two  pro- 
cesses, one  short  and  thick,,  extending  to  the  cavity  of  the  central 


Ii8 


CENTRAL   XKRVOUS  SYSTEM. 


canal,  then  being  prolonged  into  its  lumen  as  a  very  fine  ciliated 
process  ;  the  other,  or  peripheral  process,  extends  transxcrseK- 
through  the  gray  and  white  matter,  to  end  just  beneath  the  pia 
in  a  club-shaped  enlargement.  As  this  process  nears  the  pia 
it  frequently  divides  into  two  or  more   branches,  which   end   as 


Fig.  6i. — A  Section  through  the  Spin.\l  Cord  of  a  Hum.-\n  Fetls,  23  Cm.  in  Leni;th. 
Showing  the  central  canal  with  its  substantia  gelatinosa  centralis  and  ependymal  cells. — 
{After  Leiihossek.) 


above  described.  As  age  advances  this  typical  arrangement  of 
the  ependymal  cells  becomes  lost  by  atrophy  of  its  processes 
and  the  probable  transformation  of  the  ependymal  cells  into 
adult  neuroglia  cells. 

In  the  following  locations  the  neuroglia  of  the  cord  is  much 
increased  in  amount:    (i)   Around  the  entire  periphery  of  the 


SPINAL  CORD. 


119 


cord,    where  it    forms    a   distinct    mantle ;    (2)   in   the   anterior 
horns  ;  and  (3)  in  the  region  of  the  central  canal. 


THE   SUBPIAL   NEUROGLIA    LAYER,    THE    RINDENSCHICHT    OF 

THE    GERMANS. 

This  layer  consists  of   a    thick,    closely-meshed    network   of 
neuroglia  fibers,  having  interspersed  among  them  large   num- 


FiG.  62. — Transverse  Section  of  the  Spinal  Cord  of  a  Human  Embryo,  14  Cm.  in 
Length.  Illustrating  the  distribution  of  neuroglia.  On  the  right  are  seen  the  ependymal 
cells.     On  the  left,  the  neuroglia  cells. — [Aftei-  Leiihossek.) 

bers  of  neurog-lia  cells.  It  forms  a  coverinor  or  mantel  for  the 
cord,  which  varies  in  thickness  from  o.oi  to  0.06  mm.  This 
layer  is  entirely  distinct  from  the  pia  mater.  It  is  thickest  in 
the  region  about  the  anterior  and  posterior  nerve-roots,  and 
gives  oiT  fine  parallel  coursing  bundles  of  fibers,  which  accom- 
pany the  nerve-roots  for  a  short  distance.  It  is  also  quite  thick 
at  the  entrance  of  the  posterior  median  fissure,  where  a 
process,  the  posterior  median  septum,  extends  into  that  fissure 


I20  CENTRAL  NKRVOUS  SYSTEM. 

and  serves  to  divide  the  jjosterior  columns  into  synimetric 
halves,  and  conducts  blood-vessels  into  the  cord.  A  distinct 
process  of  neuroglia  exists  in  the  cervical  region,  the  posterior 
intermediate  septum,  which  separates  the  columns  of  Goll  and 
Burdach  from  each  other.  The  cells  of  this  layer  all  possess 
long  fibers,  and   are   stellate  in   shape.     The  subpial  neuroglia 


Fig.  63. — A  Transverse  Section  through  a  Segment  of  the  Dorsal  Cord  to 

SHOW  the  General  Arrangement  of  Neuroglia.     Nigrosin  stain. 

I,  I,  2,  2.  Short  and  long  neuroglia  septa.      3.   Postero-interniediate  septum.     4,  4.   Sul^pial 

neuroglia  layer. 


layer  sends  into  the  white  matter  of  the  cord  numerous  pro- 
cesses having  a  radial  course,  the  glia  septa,  which  accompany 
the  blood-vessels ;  these  processes  surround  the  vessels  and 
form  for  them  canal-like  channels.  The  neuroglia  of  the  white 
matter  of  the  cord  consists  only  of  cells  with  long  processes. 
The  fibers  of  the  white  matter,  apart  from  being  separated  by 


SPINAL  CORD.  121 

the  glia  septa  into  many  bundles,  are  separated  from  one  another 
by  a  delicate  cribriform  framework  of  neuroglia,  so  arranged 
that  each  individual  nerve-fiber  is  surrounded  by  a  neuroglia 
process.  In  the  posterior  columns  this  neuroglia  framework  is 
much  increased  in  amount.  No  ordinary  connective  tissue 
exists  in  the  cord  save  that  which  forms  the  adventitia  of  the 
blood-vessels,  and  the  pia  process  extending  into  the  anterior 
median  fissure. 


Fig.  64. — A  Camera  Lucida  Drawing  of  a  Field  of  the  Lateral  Column  of 

Figure  63.     Nigrosin  stain. 

a.   Subpial  neuroglia  layer  with  septa.      b.    Cribriform  framework  of  neuroglia.      d.  Severed 

nerve  tubes,      c.   Stellate  neuroglia  cells. 


The  neuroglia  of  the  gray  matter  differs  from  that  of  the 
white  matter  in  containing  both  varieties  of  cell.  The  antero- 
lateral horns  contain  an  abundance  of  neuroglia  cells  and  fibers, 
and  according  to  Lenhossek,  the  cells  with  short  processes  pre- 
dominate. These  horns  possess  a  rich  network  of  very  fine 
neuroglia  fibers,  in  addition  to  coarse  fibers  which  have  a  hori- 
zontal course,  and   are  arrano-ed  in  bundles  which  become  nar- 


122  CENTRAL  NERVOUS  SYSTEM. 

rowed  as  they  pass  out  with  the  anterior  nerve-roots,  while  the 
central  ends  spread  out  in  the  interior  of  the  cornua. 

Posterior  Horns. —  I  he  tip  of  the  posterior  horn  and  Lis- 
sauer's  columns  contain  a  rich  plexus  of  neuroglia  fibers,  while 
the  substantia  spongiosa  is  very  much  less  rich  in  neuroglia. 

The  Substantia  Gelatinosa  Rolandi. —  Fhis  region  of  the 
posterior  horn,  contrary  to  the  usually  accepted  opinion,  is. 
according  to  W'eigert.  very  poor  in  neuroglia,  the  few  neuroglia 
fibers  being  found  there  having  a  radial  arrangement. 

The  region  of  the  central  canal  is  rich  in  neuroglia  cells 
and  fibers.  These  are  chiefiy  arranged  in  the  form  of  a  circular 
network  just  beneath  and  around  the  central  canal.  In  front 
and  behind  the  central  canal  the  fibers  display  a  commissural- 
like  arrangement;  laterally  they  are  continuous  with  the  fibers 
of  the  anterior  horns  (Fitr.  6i ). 


THE  BLOOD  SUPPLY  OF  THE   SPINAL  CORD. 

The  arteries  which  nourish  the  cord  are  the  following:  First, 
lateral  spinal  branches  from  the  subclavian,  from  the  thoracic 
intercostals  of  the  aorta,  from  the  lumbar,  and  from  the  internal 
iliac  arteries.  Second,  the  anterior  and  posterior  spinal  branches 
of  the  vertebrals.  The  anterior  are  two  in  number,  and  arise 
from  the  vertebrals  a  little  below  their  junction  to  form  the 
basilar,  and  at  the  level  of  the  foramen  magnum  thev  unite  into 
one  vessel,  the  anterior  median  artery,  which  extends  down- 
ward, throuo^hout  the  entire  length  of  the  cord,  receiving 
branches  of  reinforcement  from  the  lateral  spinal  arteries.  This 
vessel  lies  in  the  pia  mater,  which  it  supplies,  and  it  also  gives 
off  branches  to  the  substance  of  the  cord. 

The  posterior  spinal  arteries,  two  in  number,  usually  arise  from 
the  vertebrals  at  the  sides  of  the  medulla  and  pass  backward 
to  the  dorsal  portion  of  the  medulla,  where  they  take  a  descend- 
ing course  behind  the  line  of  attachment  of  the  posterior  nerve- 
roots,  extending  downward  to  the  cauda  equina. ■•'     These  ves- 


*  The  p>osterior  spinal  arteries  occasionally  have    their  origin  from  the  posterior  inferior 
cerebellar  arteries  (Duret). 


SPINAL  CORD. 


123 


sels  receive  reinforcements  from  the  lateral  spinal  arteries 
through  the  intervertebral  foramina.  The  lateral  spinal  arteries 
after  entering  the  cord  are  designated  root  arteries.  They 
pierce  the  dura  mater,  and  send  branches  to  the  anterior  and 
posterior  nerve-roots.  The  anterior  root  arteries,  of  which  there 
are  about  eight,  are  about  twice  as  large  as  the  posterior  root 
arteries,  but  only  one-half  as  numerous.  The  more  minute 
arterial  divisions  which  supply  the  substance  of  the  cord  may 


Fig.  65. — Scheme  to  show  the  Course  and  Distribution  of  the  Terminal  Branches 

OF  the  Arterial  Plexus  of  the  Pia  Mater. — [After  Van  Gehuchten.') 

a.  spin.  post.  Posterior  spinal  arteries,     a.  spin.  ant.   Anterior  spinal  arteries,      a.  sit.   Anterior 

median  fissure,     rac.  ant.   Anterior  root  arteries. 


be  divided  into  two  sets :  first,  a  centrifugal  set,  which  is 
composed  of  a  series  of  arterioles,  about  250  in  number,  which 
come  from  the  anterior  spinal  artery  into  the  anterior  median 
fissure,  penetrating  the  anterior  commissure,  then  dividing  into 
a  right  and  a  left  branch,  which  soon  subdivide  into  smaller 
arteries  and  capillaries  for  the  central  part  of  the  gray  matter. 
Ascending  and  descending  branches  are  given  off  for  anasto- 
mosis with  the  corresponding  vessels  at  different  levels.  The 
centripetal   set  have  a  radial  arrangement,  coming  in  from  all 


124  CENTRAL  NERVOUS   SYSTEM. 

parts  of  the  periphery.  They  consist  of  short  and  lon^-  l^ranches, 
the  short  branches  supplying  the  outer  portion  oi  the  white 
matter  of  the  cord,  the  long  branches  penetrating  the  gray  matter 
and  supplying  the  parts  not  supplied  by  the  centrifugal  vessels. 
The  posterior  horns,  as  well  as  the  adjacent  white  matter  and 
cells  of  Clarke,  are  supplied  by  a  small  median  artery,  the  inter- 
funiculate,  which  passes  between  the  posterior  columns  of  each 
side  to  the  posterior  commissure  and  then  divides,  entering  the 
before-mentioned  regions.  The  posterior  fissural  artery  passes 
ventrally  through  the  posterior  median  fissure  to  supply  the 
columns  of  Goll, 

VEINS    OF    SPIXAT-    t:ORD. 

These  have  no  valves.  They  issue  from  the  interior  of  the 
cord  alongside  of  the  anterior  and  posterior  nerve-roots — 
hence  they  are  often  called  root-veins.  Of  these,  there  are 
from  forty  to  fifty  in  number — twenty-five  to  thirty  anterior,  the 
remainder  posterior.  They  pass  into  the  pia  mater,  where 
they  form  plexuses  wdiich  cover  the  entire  surface  of  the  cord, 
emerging  chiefly  from  the  anterior  and  posterior  median  fissures, 
where  they  join  the  anterior  and  posterior  longitudinal  median 
veins.  Near  the  base  of  the  skull  two  or  three  small  branches 
are  formed,  which  communicate  w^ith  the  vertebral  veins  and  then 
terminate  in  the  inferior  cerebellar  veins,  or  in  the  inferior 
petrosal  sinuses. 


CHAPTER    III. 
THE   MEDULLA   OBLONGATA,  OR    BULB. 

The  medulla  oblongata  extends  from  the  lower  border  of  the 
transverse  fibers  of  the  pons  Varolii  above  to  the  foramen 
magnum  below,  and  gradually  decreases  in  size  from  above 
downward.  It  is  somewhat  rhomboid  in  shape,  and  is  continu- 
ous below  with  the  spinal  cord.  Its  anterior  surface  rests  in  the 
basilar  groove  of  the  occipital  bone,  while  its  posterior  surface 
is  continuous  above  with  that  of  the  pons  Varolii,  and  lies  be- 
tween the  hemispheres  of  the  cerebellum,  in  a  fossa  called  the 
vallecula,  or  little  valley.  Issuing  from  it  are  the  lower  six 
pairs  of  cranial  nerves. 

The  medulla  is  divided  into  symmetric  halves  by  the  ex- 
tension upward  of  the  anterior  and  posterior  median  fissures  of 
the  cord.  The  anterior  median  fissure  contains  a  fold  of  pia 
mater,  and  continues  upward  to  just  below  the  pons,  where  it 
ends  in  a  small  fossa,  the  foramen  caecum.  It  is  interrupted 
below  by  the  motor  or  pyramidal  decussation.  The  posterior 
fissure  is  a  deep  but  narrow  fissure,  and  continues  upward  to 
about  the  middle  of  the  medulla,  where,  owing  to  the  diverg- 
ence of  the'  posterior  columns,  it  becomes  lost  on  the  floor  of 
the  fourth  ventricle. 

The  medulla  may  be  divided  into  anterior,  lateral,  and  pos- 
terior columns,  which  are  continuations  upward  of  the  corre- 
sponding columns  of  the  spinal  cord.  The  columns,  together 
with  special  deposits  of  nervous  matter  peculiar  to  the  medulla, 
give  to  it  its  outward  configuration.  The  anterior  columns,  or, 
more  properly,  the  anterior  pyramids  of  the  medulla,  lie  between 
the  anterior  median  fissure  and  the  exit  of  the  hypoglossal  or 
twelfth  pair  of  cranial  nerves  below,  and  the  exit  of  the  sixth 

pair  above.     The  exact  line   of  division  between  the   anterior 

125 


126  CENTRAL    XKRVOUS   SYSTEM. 

pyramids  and  tlie  lateral  columns  is  the  ventrolateral  groove, 
which  is  the  direct  continuation  upward  of  the  line  of  emergence 
of  the  anterior  nerve-roots  of  the  spinal  cord.  The  anterior  col- 
umns of  the  cord  are  continued  upward  into  the  medulla  in  the 
same  relative  position  on  each  side  of  the  anterior  median 
fissure.  They  form  only  a  small  number  of  the  fibers  present 
at  or  above  the  motor  or  pyramidal  crossing. 

In  the  spinal  cord  were  noted  two  distinct  divisions  of  the 
motor  or  pyramidal  tracts,  one  coming-  down  in  the  anterior 
column,  adjacent  to  the  anterior  median  fissure,  known  as  the 
direct  pyramidal  or  motor  tract ;  the  other,  much  greater  in 
size,  occupying  a  large  area  in  the  posterior  part  of  the  lateral 
column  of  the  cord,  known  as  the  crossed  pyramidal  or  motor 
tract  because  of  having-  crossed  in  the  medulla.  These  two 
bundles,  direct  and  crossed  motor  tracts,  form  the  anterior  col- 
umns or  pyramids  of  the  medulla. 

The  lateral  columns,  or  lateral  areas  of  the  medulla,  lie  between 
the  exit  of  the  hypoglossal  nerves  or  the  ventrolateral  grooves  in 
front  and  the  exit  of  the  spinal  accessory,  pneumogastric,  and 
glossopharyngeal  nerves  behind,  which  nerves  issue  from  the 
dorsolateral  grooves,  which  are  the  continuation  upward  of  like- 
named  grooves  existing  in  the  cord.  The  olivary  bodies  are 
embedded  in  the  upper  part  of  the  lateral  area.  The  lateral 
columns  are  continuations  upward  of  the  corresponding  columns 
of  the  cord,  but  the  latter  are  not  preserved  as  such  in  their 
entirety,  owing  to  the  fact  that  the  fibers  of  the  crossed  pyramidal 
tracts  leave  their  position  to  form  the  motor  decussation,  and  the 
direct  cerebellar  tracts  or  columns  of  Flechsig  gradually  trend 
backw^ard  and  unite  with  the  restiform  bodies  to  pass  into  the 
cerebellum. 

The  posterior  area  of  the  medulla  is  a  continuation  upward 
of  the  posterior  columns  of  the  spinal  cord,  which  have  gradually 
increased  in  size  from  below  upward.  This  area  is  subdivided 
by  a  neuroglia  process — the  postero-intermediate  septum — into 
the  inner  or  column  of  Goll,  and  the  outer  or  column  of  Burdach, 
which  in  turn  are  separated  from  the  lateral  area  of  the  medulla  by 
the  dorsolateral  groove.  The  former  passes  upward,  the  fibers 
of  which  it  is  composed  ending  about  a  collection  of  ganglionic 


Fig.  66. — View  from  Before  of  the  Medulla  Oblongata,  Pons  Varolii,  Crura 
Cerebri,  and  other  Central  Portions  of  the  Encephalon  (Natural  size). — 
i^Allen   Thomson.')  —  {Frofii  Qiiahi' s  ''Anatomy.'") 

On  the  right  side  the  convolutions  of  the  central  lobe,  or  island  of  Reil,  have  been  left,  together 
with  a  small  part  of  the  anterior  cerebral  convolutions  ;  on  the  left  side  these  have  been 
removed  by  an  incision  carried  betvfeen  the  thalamus  opticus  and  the  cerebral  hemisphere. 

V.  The  olfactory  tract  cut  short  and  lying  in  its  groove.  II.  The  left  optic  nerve  in  front  of  the 
commissure.  IF.  The  right  optic  tract.  77^  The  cut  surface  of  the  left  thalamus  opticus. 
C.  The  central  lobe  or  island  of  Reil.  Sy.  Fissure  of  Sylvius.  X  X-  Anterior  perforated 
space,  e.  The  external  corpus  geniculatum.  i.  The  internal  corpus  geniculatum.  h.  The 
hypophysis  cerebri  or  pituitary  body.  ic.  Tuber  cinereum  with  the  infundibulum.  a.  One 
of  the  corpora  albicantia.  P.  The  cerebral  peduncle  or  crus.  III.  Close  to  the  left  oculo- 
motor nerve.      X-   The  posterior  perforated  space. 

The  following  letters  and  numbers  refer  to  parts  in  connection  with  the  medulla  oblongata  and 
pons.  PV.  'Pons  Varolii.  V.  The  greater  root  of  the  fifth  nerve.  +.  The  lesser  or 
motor  root.  Vf.  The  sixth  nerve.  VII.  The  facial.  V/II.  The  auditory  nerve.  XI. 
The  glossopharyngeal.  A'.  The  pneumogastric  nerve.  XI.  The  spinal  accessory  nerve. 
XII.  The  hypoglossal  nerve.  C  I.  The  suboccipital  or  first  cervical  nerve.  /  a.  Pyra- 
mid, o.  Olive,  d.  Anterior  median  fissure  of  the  spinal  cord,  above  which  the  decussa- 
tion of  the  pyramids  is  represented,  c  a.  Anterior  column  of  cord.  r.  Lateral  tract  of 
bulb  continuous  with  c  I,  the  lateral  column  of  the  spinal  cord. 

127 


Fig.  67. — View   of  the  Medulla  Oblongata,   Pons  Varolii,    Crura   Cerebri,  and 

Central  Parts  of  the  Encephalon  from  the  Right  Side. — [AHen  Thomson.) 

{^Frofn  Quain' s  '^ Anatomy y) 

The  corpus  striatum  and  thalamus  opticus  have  been  preserved  in  connection  with  the  central 
lobe  and  crura  cerebri,  while  the  remainder  of  the  cerebrum  has  been  removed. 

Si.  Upper  surface  of  the  corpus  striatum.  Tk.  Back  part  of  the  thalamus  opticus  (pulvinar). 
C.  Placed  on  the  middle  of  the  five  or  six  convolutions  constituting  the  central  lobe  or 
island  of  Reil,  the  cerebral  substance  being  removed  from  its  circumference.  Sv.  Fissure 
of  Sylvius,  from  which  these  convolutions  radiate,  and  in  which  are  seen  the  white  strife  of 
the  olfactory  tract.  I.  The  olfactory  tract  divided  and  hanging  down  from  the  groove  in 
the  convolution  which  lodges  it.  II.  Optic  nerves  a  little  way  in  front  of  the  commissure. 
a.  Right  corpus  albicans  with  the  tuber  cinereum  and  infundibulum  in  front  of  it.  k.  Hy- 
pophysis or  pituitary  body.  e.  External,  and  i,  internal,  corpus  geniculatum  at  the  back 
part  of  the  optic  tract.  P.  Peduncle  or  crus  of  the  cerebrum.  III.  Right  oculomotor 
nerve,  p.  Pineal  gland,  q.  Corpora  quadrigemina.  IV.  Trochlear  nerve  rising  from  v, 
the  valve  of  Vieussens. 

The  following  numbers  and  letters  refer  chiefly  to  parts  in  connection  with  the  medulla  oblongata 
and  pons.  V.  Placed  on  the  pons  Varolii  above  the  right  nervus  trigeminus,  s.  The  su- 
perior, m,  the  middle,  and  in,  the  inferior  peduncle  of  the  cerebellum  cut  short.  VI.  The 
sixth  nerve.  VII.  Facial  nerve.  VIII.  Auditory  nerve.  IX.  The  glossopharyngeal 
nerve.  X.  Placed  opposite  to  the  cut  end  of  the  pneumogastric  nerve.  XI.  The  upper- 
most fibers  of  the  spinal  accessory  nerve.  XII.  The  hypoglossal  nerve,  p  a.  Pyramid. 
0.  Olive,  a  r.  Arciform  fibers,  r.  Restiform  body.  tr.  Tubercle  of  Rolando,  c  a. 
Anterior,  c  p,  posterior,  and  c  /,  lateral  columns  of  the  spinal  cord.  CI,  Ci.  Anterior  and 
posterior  roots  of  the  first  cervical  nerve. 

9  129 


THE   MEDULLA  OBLONGATA,  OR   BULB.  131 

nerve-cells,  which  form,  on  the  posterior  aspect  of  the  medulla, 
a  distinct  prominence,  known  as  the  nucleus  of  the  column  of 
Goll,  or  the  nucleus  gracilis.  This  collection  of  nerve-cells 
at  the  lower  part  of  the  fourth  ventricle  on  each  side  is 
called  the  clava,  or  key,  from  its  shape.  These  clavae  diverge 
and,  with  the  restiform  bodies,  assist  in  forming  the  postero- 
lateral boundary  of  the  fourth  ventricle.  The  fibers  of  the 
outer  column,  or  column  of  Burdach,  end  about  a  collection  of 
nerve-cells,  located  lateral  to  the  nucleus  gracilis,  which  collec- 
tion is  called  the  nucleus  cuneatus,  or  wedge.  Both  these 
nuclei  are  inseparably  blended  above.  The  columns  of  Goll 
and  Burdach,  with  their  end  nuclei,  are  sometimes  called  the 
posterior  pyramids.  Just  external  to  the  nucleus  cuneatus,  and 
between  it  and  the  exit  of  the  spinal  accessory  nerves,  exists  an 
eminence  on  each  side,  due  to  a  marked  increase  of  the  sub- 
stantia gelatinosa,  capping  the  posterior  horn,  called  the  tubercle 
of  Rolando. 

The  restiform  bodies  (from  the  Latin  restis,  a  rope)  are  the 
largest  prominences  of  the  medulla,  seeming,  from  the  appear- 
ances of  transverse  sections  at  the  lower  part  of  the  medulla, 
to  occupy  the  upward  extension  of  the  posterior  and  a  large 
part  of  the  lateral  columns,  from  both  of  which  they  receive 
many  fibers.  They  diverge,  assisting  in  the  formation  of  the 
lateral  boundaries  of  the  fourth  ventricle,  and  pass  into  the 
cerebellar  hemispheres  as  the  inferior  cerebellar  peduncles. 


THE  FOURTH  VENTRICLE. 

The  fourth  ventricle  is  the  space  located  between  the  poste- 
rior surfaces  of  the  pons  Varolii  and  medulla  oblongata  in 
front  and  the  cerebellum  behind.  Into  this  space  the  central 
canal  of  the  spinal  cord  broadens  out,  and  the  space  may  be 
regarded  as  an  expansion  of  that  canal.  It  is  rhomboid  in 
shape,  and  has  for  its  floor  the  posterior  surfaces  of  the  medulla 
and  pons,  and  for  its  roof,  which  is  somewhat  arched,  the 
superior  and  inferior  medullary  vela,  together  with  a  process 
of  pia  mater,  the  tela  choroidea  inferior,  for  the  lower  part.  The 
superior  medullary  velum,  or,  as  it  is   sometimes  termed,   the 


132  CENTRAL  NERVOUS  SYSTEM. 

valve  of  Vieussens,  is  a  lamina  of  white  matter  from  the  middle 
lobe  or  worm  of  the  cerebellum  which  arches  across  from  one 
superior  cerebellar  peduncle  to  the  other.  The  inferior  medul- 
lary velum  is  likewise  a  process  of  white  matter  coming  from 
the  same  source.  The  process  of  pia  mater  above  referred  to 
is  a  reflection  of  that  membrane  from  the  under  surface  of  the 
inferior  medullary  velum  to  supply  the  interval  left  by  the  latter. 
This  process  of  pia  mater  is  lined  by  a  layer  of  epithelium 
which  is  continuous  below,  and  at  its  sides,  with  that  lining  the 
cavity  of  the  ventricle,  and  is  perforated  along  its  median  line 
by  an  opening,  the  foramen  of  Magendie,  which  connects  this 
cavity  with  the  subarachnoid  space  surrounding  the  spinal 
cord.  This  opening  is  just  above  the  point  where  the  central 
canal  opens  into  the  fourth  ventricle.  Before  this  epithelial 
layer  mentioned  above  reaches  the  lateral  boundaries  of  the 
ventricle  it  is  somewhat  thickened  by  an  accession  of  white 
matter,  this  thickenino-  startincr  at  the  inner  martrin  toward  the 
apex  of  the  clava,  coursing  along  the  lateral  boundary  of  the 
ventricle,  crossing  the  restiform  body,  and  ending  at  the  exit  of 
the  vagus  and  glossopharyngeal  nerves  ;  it  is  called  the  tenia, 
or  ligula.  Just  above  the  calamus  scriptorius,  at  the  apex  of  the 
ventricle,  and  occupying  the  interval  between  the  clavae,  there  is 
another  thickening  of  white  matter,  called  the  obex.  The  widest 
part  of  the  ventricle  extends  on  each  side  between  the  cere- 
bellum and  medulla,  forming  the  lateral  recesses,  the  lower 
boundary  of  each  being  the  ligula.  The  superior  border  of  this 
ventricle  is  formed  on  each  side  by  the  superior  cerebellar 
peduncles,  coming  from  the  region  of  the  corpora  quadrigemina 
above,  and  passing  downward  and  diverging  in  their  course  to 
the  cerebellum. 

The  inferior  borders  are  formed  by  the  diverging  posterior 
columns  of  the  medulla  and  the  restiform  bodies.  The  fourth 
ventricle  at  its  upper  angle  communicates  with  the  space  above 
— the  third  ventricle — by  means  of  a  narrow  passage  known  as 
the  Sylyian  aqueduct.  This  passage  is  nearly  two  cm.,  or  about 
three-fourths  of  an  inch,  in  length  ;  on  transverse  section  near  the 
medulla  it  is  T-shaped,  becoming  oval  in  the  middle  of  its  course, 
and  triangular  as  it  opens  into  the  third  ventricle.     It  is  lined  with 


S.TTt.V     \    \    yp      \     \     \         1^     /      O 


Fig.  68. — Posterior  and  Lateral  View  of  the  Medulla  Oblongata.  Fourth  Ven- 
tricle and  Mesencephalon  (Natural  size).  —  {E.A.S.) — {From  Quains  "Anatomy.'") 

The  cerebellum  and  inferior  medullary  velum,  and  the  right  half  of  the  superior  medullary 
velum,  have  been  cut  away  so  as  to  expose  the  fourth  ventricle. 

p.n.  Line  of  the  posterior  roots  of  the  spinal  nerves,  p.m.f.  Posterior  median  fissure,  f.g. 
Funiculus  gracilis,  cl.  Its  clava.  f.c.  Funiculus  cuneatus.  f.R.  Funiculus  of  Rolando. 
r.b.  ReSliform  body.  c.s.  Lower  end  of  the  fourth  ventricle  (calamus  scriptorius).  /. 
Section  of  the  lingula  or  tenia ;  part  of  the  choroid  plexus  is  seen  beneath  it.  l.r.  Lateral 
recess  of  the  ventricle,  str.  Striae  acusticse.  i.f.  Inferior  (posterior)  fovea,  s.f.  Superior 
(anterior)  fovea;  between  it  and  the  median  sulcus  is  the  funiculus  teres,  cbl.  Cut  surface 
of  the  left  cerebellar  hemisphere,  n.d.  Central  gray  matter  (nucleus  dentatus)  seen  as  a 
wavy  line,  s.m.v.  Superior  (anterior)  medullary  velum.  Ing.  Lingula.  s.c.p.  Superior 
cerebellar  peduncle  cut  longitudinally,  cr.  Combined  section  of  the  three  cerebellar 
peduncles  (the  limits  of  each  are  not  marked),  c.q.s.,  c.q.i.  Corpora  quadrigemina  (superior 
aud  inferior),  fr.  Fraenulum  veli.  f.  Fibers  of  the  fillet  seen  on  the  surface  of  the  teg- 
mentum, c.  Crusta.  l.g.  Lateral  groove,  c.g.i.  Corpus  geniculatum  internum,  th. 
Posterior  part  of  thalamus,  p.  Pineal  body.  The  Roman  numbers  indicate  the  corres- 
ponding cranial  nerves. 

133 


THE   MEDULLA  OBLONGATA,  OR   BULB.  135 

columnar  ciliated  epithelium,  the  basal  surfaces  of  which  cells  are 
probably  connected  by  radiating  processes  with  the  underlying 
neuroglia  cells.  The  floor  of  the  ventricle  has,  in  general,  the 
shape  of  two  triangles  placed  base  to  base  ;  it  is  lined  with  ciliated- 
epithelium — the  ependyma  (Greek  ^rd  ivdoim,  a  close-fitting  gar- 
ment)— resting  upon  an  underlying  neuroglia  matrix,  and  is 
continuous  with  the  lining  of  the  aqueduct  of  Sylvius.  At  the 
apex  of  the  upper  triangle  is  the  opening  of  the  Sylvian  aque- 
duct. Just  below,  in  the  median  line,  begins  a  fissure  (the 
median)  which  extends  downward  nearly  to  the  apex  of  the 
lower  triangle,  to  terminate  in  an  opening — the  ventricle  of 
Arantius.  On  each  side  of  this  fissure  is  seen  a  loneitudinal 
eminence  which  extends  throughout  the  entire  length  of  the 
ventricle.  It  is  more  prominent  above,  and  becomes  gradually 
indistinct  below.  These  eminences  consist  of  a  few  nerve-fibers, 
together  with  the  bases  of  the  anterior  horns  of  gray  matter, 
which  have  come  to  the  surface  of  the  ventricle  after  the  spinal 
canal  has  opened  into  it.  They  are  made  up  of  a  large  number 
of  multipolar  cells,  whose  axones  form  the  root-fibers  of  the 
hypoglossal  nerves  below  and  the  abducens  or  sixth  pair  of 
cranial  nerves  above.  These  eminences  have  received  the 
name  of  fasciculi  or  funiculi  teretes.  The  white  fibers  of  which 
each  fasciculus  is  composed  are  the  ascending  part  of  the  facial 
nerve  and  some  fibers  of  the  formatio  reticularis. 

At  about  its  widest  point  the  floor  of  the  ventricle  is  crossed 
by  several  white  streaks,  called,  from  their  relation  to  the  audi- 
tory nerve,  the  striae  acousticae.  Just  outside  of  the  median 
groove,  and  above  these  striae,  is  a  small  fossa  on  each  side — the 
fovea  superior;  while  below  these  striae  is  a  small  triangular 
depression, — the  fovea  inferior, — the  base  of  which  is  divided  into 
two  grooves,  the  inner  one  of  which  passes  to  the  lower  inferior 
angle  of  the  ventricle,  the  outer  one  passing  obliquely  down- 
ward to  the  lateral  border  of  the  same.  Between  these  two 
grooves  exists  another  triangle,  much  darker  than  the  adjoining 
gray  matter,  called  the  ala  cinerea  (ash-colored  wing),  the  apex 
of  which  is  depressed,  but  its  lower  portion  is  distinctly  promi- 
nent, and  is  termed  the  eminentia  cinerea.  This  eminence 
contains   the   sensory   end   nuclei    for    the    pneumogastric   and 


136  CENTRAL  NERVOUS  SYSTEM. 

glossopharyngeal  nerves.  At  the  lower  portion  of  the  floor  of 
the  ventricle,  where  the  posterior  columns  begin  to  diverge,  a 
small  triangular  space  is  formed,  at  the  lower  end  of  which  is 
the  ventricle  of  Arantius.  This  space  is  called  the  calamus 
scriptorius,  "writing-pen,"  from  its  resemblance  to  a  pen. 
This  resemblance  is   further  heightened  by  the  median  groove. 

The  following  cranial  nerves  have  their  points  of  exit  from  the 
medulla,  given  in  the  order  in  which  they  leave,  starting  from 
above.  The  sixth  pair,  called  the  abducens,  issue  from  the  junc- 
tion of  the  pons  and  medulla  between  the  anterior  pyramids  and 
the  olivary  bodies,  coming  from  the  upper  end  of  the  ventro- 
lateral groove,  and  cross  the  anterior  surface  of  the  pons  near 
its  middle. 

The  seventh,  or  facial,  and  the  eighth,  or  auditory,  nerves 
emerge  at  the  periphery  of  the  medulla  near  its  junction  with 
the  pons,  from  a  depression  between  the  olivary  and  restiform 
bodies,  the  former  being  within  and  above  the  latter. 

The  roots  of  the  ninth,  or  glossopharyngeal,  and  the  tenth,  or 
pneumogastric,  nerves  have  their  points  of  exit  on  each  side 
external  to  the  olivary  bodies  in  a  groove — the  dorsolateral — 
located  between  the  lateral  column  and  restiform  body,  which 
corresponds  to  the  dorsolateral  groove  of  the  spinal  cord.  The 
upper  five  or  six  filaments  belong  to  the  glossopharyngeal,  while 
the  lower  ones,  twelve  to  fifteen,  belong  to  the  pneumogastric. 

The  eleventh  pair,  or  spinal  accessory  nerves,  which  consist 
of  several  distinct  strands  of  nerve-fibers  coming  from  the 
medulla  and  the  cervical  part  of  the  spinal  cord  as  low  down  as 
the  fifth  or  sixth  cervical  segment,  pass  out  dorsal  to  the  olivary 
bodies  from  the  dorsolateral  groove  in  the  same  plane  as  the 
pneumogastric  and  glossopharyngeal  nerves. 

The  twelfth  pair,  or  hypoglossal  nerves,  consist  of  a  dozen  or 
more  fine  root-fibers  which  have  their  point  of  emergence  in  a 
groove — the  ventrolateral — located  between  the  anterior  pyra- 
mids and  the  olivary  bodies.      (See  Fig.  66,  p.  127.) 

While,  in  reality,  the  medulla  oblongata  is  an  upward  con- 
tinuation of  the  spinal  cord,  it  differs  essentially  from  the  cord 
in  its  shape,  owing  to  the  development  of  new  gray  matter,  to  the 


THE   MEDULLA  OBLONGATA,  OR   BULB.  137 

widening  of  the  spinal  canal  into  the  fourth  ventricle,  and  to  the 
changed  position  of  the  various  tracts  proceeding  from  the  cord. 


A  TRANSVERSE  SECTION  OF   THE  MEDULLA  AT  THE 
LEVEL  OF  THE  FIRST  CERVICAL  NERVE. 

The  transition  of  the  cervical  part  of  the  spinal  cord  into  the 
medulla  is  a  very  gradual  one.  A  section  at  this  level  differs  from 
a  section  in  the  upper  cervical  region  only  in  the  following  par- 
ticulars :  The  posterior  horns  are  much  lengthened  and  nar- 
rowed, and  present  at  their  ends,   or  capita,  globular  enlarge- 


X-' 


Fig.  69. — Transverse  Section  through  the  Medulla  Oblongata  at  the  Beginning 
OF  the   Motor  Decussation. — [Afiei-  Koelliker.) 

ments  which  are  due  to  a  marked  increase  of  the  substantia 
gelatinosa  of  Rolando.  The  caput,  with  its  substantia  gelatinosa, 
produces  on  each  side  an  external  prominence — the  tubercle 
of  Rolando.  It  is  composed  of  a  rich  network  of  neuroglia 
fibers,  among  which  exists  a  number  of  large  and  small  cells, 
probably  sensory  in  function.  It  is  permeated  by  a  number  of 
fine  fibers,  which  are  located  external  to  it,  near  the  periphery  of 
the  medulla,  and  which  appear  on  cross-section  as  a  crescentic 
bundle  of  longitudinal  fibers  that  occupy  the  same  relative  posi- 
tion until  they  reach  the  middle  of  the  pons,  where  they  emerge, 
forming  the  so-called  ascending,  but  in  fact  descending,  root  of 


138 


CENTRAL  NERVOUS  SYSTEM. 


AP    r.^Af    l.O.L. 
Fig.  70. 


the  fifth  or  trigeminal  nerve.  These 
fibers,  with  their  collaterals,  are  the 
central  axones  of  the  cells  of  the 
Gasserian  ganglion  of  each  side. 
These  axones  consist  of  two  sets  : 
those  having  a  long  course,  and 
those  having  a  short  course.  TJie 
former,  with  their  collaterals,  end 
in  brush-like  expansions  about  the 
small  sensory  cells  existing  in  the 
head  of  the  posterior  horns,  which 
may  be  considered  as  the  end 
nuclei  for  the  axones.  From  the 
cells  of  the  posterior  horns  new 
axones  start  out,  and  after  crossing 
in  the  raphe,  they  pass  into  the 
fillet  or  lemniscus  of  the  opposite 
side  and  continue  brainward,  form- 
ing the  central  sensory  tract  of  the 
triofeminal  nerve.  The  axones  of 
short  course,  with  their  collaterals, 
probably  subserve  a  reflex  function, 
and  end  about  the  motor  nuclei  of 
the  trigeminal,  facial,  glossopharyn- 
geal, and  possibly  of  the  pneumo- 

FiG.  70. — Diagrams  of  the  Structure  of  the 
Medulla  Oblongata. — {From  Gower's  "Dis- 
eases of  the  Nei-votts  System.'") 

A.  Lower,  and  B,  upper,  part  of  decussation  of  the 
pyramids.  C.  At  the  lowest  of  the  olivary  bodies. 
D.  At  the  apex.  E.  At  the  middle  of  the  cala- 
mus scriptorius.  A.  Anterior.  L.  Lateral 
column  of  cord.  A.  P.  Ant.  pyramid.  R.  Resti- 
form  body.  a.c.  Ant.  cornu.  tH.  Tubercle  of 
Rolando,  c.c.p.  Caput  cornu  posterioris.  d.c.t. 
Direct  cerebellar  tract.  Ny.  Hypoglossal  nerve. 
//)'.  fiti-  Its  nucleus.  01.  Olivary  body,  p.m.c. 
Post.  med.  col.  p-e.c.  Post.  ext.  col.  p.m.n. 
Post.  med.  nucleus,  p.e.n.  Post.  ext.  nucleus. 
Sp.A.  Spinal  accessory  nerve;  sp.a.mi.  Its  nu- 
cleus, s.c.  Slender  column.  V.as.  Ascending 
root  of  the  fifth  nerve. 


THE   MEDULLA  OBLONGATA,  OR   BULB.  139 

gastric  nerves.  The  cells  of  the  Gasserian  ganglia  may  be  re- 
garded as  the  centers  of  origin  of  the  sensory  portion  of  the  fifth 
pair  of  cranial  nerves.  They  are  analogous  to  the  posterior  spinal 
ganglia,  and  contain  cells  which  give  off  peripheral  and  central 
axones.  The  central  axones  bifurcate  on  reaching  the  pons  Va- 
rolii, one  branch  passing  slightly  upward,  to  enter  the  enlarged  ter- 
mination of  the  head  of  the  posterior  horn,  the  other  downward. 
These  latter  fibers — i.  e.,  those  havinor  a  downward  course — form 
the  crescentic  bundles  before  mentioned,  and  occupy  an  area 
outside  of  the  head  of  the  posterior  horn  on  each  side.  Former 
anatomists  termed  this  bundle  of  fibers  the  ascending  root  of 
the  fifth  pair,  but  recent  investigation  has  showm,  as  above,  that 
in  reality  the  fibers  have  a  downward  course. 

The  posterior  horns  diverge,  trending  forward  and  outward, 
thus  producing  a  broadening  out  of  the  gray  matter.  At  this 
level  the  lateral  horns  have  attained  their  greatest  size,  and  pro- 
ject outward  into  the  lateral  area,  producing  distinct,  somewhat 
triangular,  masses  of  gray  matter.  At  their  base,  and  near  their 
ventral  portion,  exists  a  collection  of  multipolar  nerve-cells 
which  form  a  distinct  column  on  each  side.  These  columns 
have  a  considerable  vertical  extent,  and  their  axones  form  the 
root-fibers  of  the  spinal  accessory  or  eleventh  pair  of  cranial 
nerves.* 

Koelliker  believes  that  this;group  of  cells,  whose  axones  form 
the  spinal  portion  of  the  eleventh  pair  of  cranial  nerves,  really 
belongs  to  the  base  of  the  anterior  horns.     There  is  a  marked 


*  The  Spinal  Accessory  or  Eleventh  Pair  of  Cranial  Nerves.— The  eleventh  or  spinal 
accessory  nerve  of  each  side  consists  of  tw;o  portions,  the  spinal  and  the  (accessorius  vagi) 
bulbar  accessory.  The  accessorius  vagi,  or  bulbar  accessory  portion  of  this  nerve,  takes  its 
origin  from  the  most  inferior  part  of  the  nucleus  ambiguus,  or  the  combined  motor  nucleus  for 
the  pneumogastric  and  glossopharyngeal  nerves.  The  axones  from  the  cells  of  this  nucleus 
pass  outward  through  the  lateral  field  of  the  medulla  ventral  to  the  crescentic  bundle  of  tri- 
geminal (descending)  nerve-fibers,  forming  four  or  five  fasciculi  of  fibers  which  emerge  from  the 
dorsolateral  groove  of  the  medulla  in  the  same  plane  with  the  pneumogastric  and  glosso- 
pharyngeal nerves.  These  fasciculi  now  unite  with  the  spinal  portion  of  this  nerve,  and, 
after  passing  through  the  jugular  foramen,  separate  from  the  spinal  portion  and  join  the  trunk 
ganglion  of  the  pneumogastric  nerve,  and  are  distributed  mainly  with  the  pharyngeal  and 
superior  laryngeal  branches  of  that  nerve. 

The  spinal  portion  of  this  nerve  on  each  side  takes  its  origin  from  a  group  of  nerve-cells 
existing  at  the  junction  of  the  lateral  with  the  anterior  horns.  This  column  of  cells  extends 
from  the  level  of  the  fifth  to  the  first  cervical  nerve.     The  axones  from  the  cells  of  this  nucleus 


I40  CENTRAL  NERVOUS  SYSTEM. 

growth  of  the  processus  reticularis  at  the  side  of  the  gray  matter, 
ventral  to  the  posterior  horns,  this  growth,  together  with  the 
forward  movement  of  the  posterior  horns,  crowding  the  lateral 
horns  nearer  to  the  anterior  horns. 


A  SECTION  AT  THE  LEVEL  OF  THE  MOTOR  CROSSWAY. 

At  this  level,  as  the  name  implies,  can  be  seen  the  lowermost 
decussation  of  the  medulla,  known  as  the  motor  or  pyramidal 
decussation.  Throughout  the  spinal  cord,  in  the  posterior  part 
of  the  lateral  columns,  exist  the  crossed  motor  or  pyramidal 
tracts.  As  the  cord  gradually  passes  into  the  medulla,  the 
fibers  of  these  tracts,  from  each  side,  leave  their  positions  in  the 
lateral  columns,  pass  obliquely  through  the  gray  matter  of  the 
medulla,  decussate  with  the  corresponding  fibers  of  the  opposite 
side,  and  unite  anteriorly  with  the  direct  or  uncrossed  motor  or 
pyramidal  tracts,  forming  a  large,  broadly  triangular  field  of 
longitudinal  fibers  on  the  ventral  aspect  of  the  medulla,  known 
as  the  anterior  pyramids.  These  fibers  continue  brainward  as 
the  motor  tracts,  to  end  in  the  motor  area  of  the  cerebral  cortex. 
Thus,  if  we  trace  upward  the  left  motor  tract  of  the  cord,  it 
crosses  over  in  the  motor  crossway  and  unites  with  the  direct 
pyramidal  tract  of  the  right  side,  forming  in  the  medulla  the 
right  pyramid,  the  fibers  of  which  pass,  as  we  shall  see  later,  to 
the  right  motor  area  of  the  brain.  A  destruction  of  this  tract, 
either  at  its  beginning  in  the  brain  or  at  any  point  above  the 
motor  crossing,  produces  a  paralysis  of  the  left  side  of  the  body, 

pass  outward  through  the  lateral  column,  between  the  posterior  nerve-roots  and  the  ligamentum 
denticulatum,  emerging  from  the  cord  in  the  dorsolateral  groove.  They  form  a  series  of 
nerve-filaments  extending  from  the  fifth  to  the  first  cervical  nerve.  The  filaments  now  unite 
to  form  a  round  bundle  of  fibers,  which  pass  brainward  and  enter  the  cranial  cavity  through  the 
foramen  magnum.  Here  they  are  joined  by  the  accessory  or  bulbar  portion.  They  then  turn 
outward  to  enter  the  middle  compartment  of  the  jugular  foramen,  in  common  with  the  pneumo- 
gastric,  being  separated  from  the  latter  nerve  by  a  fold  of  the  arachnoid.  At  their  exit  through 
the  jugular  foramen  they  pass  downward,  backward,  and  outward  between  the  occipital  artery 
and  internal  jugular  vein.  They  then  descend  behind  the  digastric  and  stylohyoid  muscles  and, 
piercing  the  sternomastoid  muscle,  pass  obliquely  across  the  posterior  triangle  of  the  neck, 
terminating  deep  within  the  trapezius  muscle.  In  their  course  they  give  off  several  branches  to 
the  sternomastoid,  and  join  in  that  muscle  the  second  cervical  nerve.  In  the  posterior  triangle 
they  are  joined  by  the  third  and  fourth  cervical  nerves  to  form  the  subtrapezial  plexus  for  the 
supply  of  the  trapezius  muscle. 


THE   MEDULLA  OBLONGATA,  OR   BULB. 


141 


and  the  tract  itself  undergoes  a  secondary  descending  degen- 
eration throughout  its  entire  extent.  In  order  to  avoid  con- 
fusion, the  motor  tract  has  been  traced  from  below  upward, 
while  in  reality  its  actual  course  and  conduction  of  impulses  is 
downward — i.  e.,  from  the  brain  to  the  cord.  It  may  be  stated  here 
that  while  most  of  the  fibers  actually  decussate  in  the  motor 
crossway,  it  has  been  proved    by  several    observers  that   the 


Fig.  71. — Transverse  Section  of  the  Medulla  Oblongata  through  the  Motor 

Decussation. — [After  Henle.) 

Fpy.   Anterior  pyramid.      Cga.   Anterior  horn.     Fa.    Remains  of  the  anterior  column.      Ng. 

Nucleus  gracilis,     g.   Substantia  gelatinosa.     XL    Spinal  accessory  nerve. 

decussation  is  not  complete  ;  that  in  many  instances  a  minority 
of  the  fibers  do  not  decussate,  but  pass  downward  in  the  lateral 
column  of  the  same  side.  This  explains  an  interesting  fact  long 
observed  :  that  in  some  cases  of  hemiplegia  the  unaffected  side, 
especially  the  leg,  is  distincdy  weaker  than  normal,  and  presents 
exaggeration  of  the  deep  reflexes  ;  this  clinical  fact  seems  to 
prove  that  the  decussation  is  incomplete  and  that  a  number  of 
fibers  pass  down  the  cord  on  the  same  side  as  the  lesion. 


142 


CENTRAL  NERVOUS  SYSTEM. 


Owing  to  the  motor  decussation,  a  part  of  each  anterior  liorn 
becomes  completely  severed  from  its  connection  with  the  rest 
of  the  gray  matter  and  is  gradually  pushed  outward  and  back- 
ward, and  comes  to  occupy  a  small  space  a  little  ventrad  to  the 
head  of  the  posterior  horn.  The  anterior  horns  continue  up- 
ward in  this  same  relative  position  to  the  pons,  where  they 
gradually  become  lost.     The  bases  of  the  horns  remain  with  the 


Fig.  72. — Transverse  Secfion   of  the  Medulla  at  the  Beginning  of   Hypoglossal 

Nerves.     The  pyramidal  or  motor  decussation  is  complete. — {After  J/ettle.) 

Ng.    Nucleus  gracilis.       Nc.    Nucleus  cuneati.       g.    Substantia  gelatinosa  of  posterior  horn. 

XII.    Hypoglossal  nerve-roots.     Fpy.   Anterior  pyramid.      Fa.   Remains  of  anterior  column. 


multipolar  nerve-cells  connected  with  the  gray  matter,  and 
owing  to  the  spreading  out  of  the  latter,  they  come  to  lie  dorso- 
lateral to  the  central  canal.  The  neuraxones  of  these  multipolar 
cells  form  the  root-fibers  of  the  hypoglossal  or  twelfth  pair  of 
cranial  nerves.  The  space  left  in  each  lateral  area  of  the 
medulla,  owino-  to  the  loss  of  fibers  resulting  from  the  motor 
decussation,  is  in  part  filled  by  the  interposition   of  the  lower- 


THE  MEDULLA  OBLONGATA,  OR   BULB. 


143 


most  part  of  a  new  mass  of  gray  matter, — the  olivary  body, — 
and  in  part  by  the  posterior  horn,  which  has  trended  forward. 

In  sections  just  above  the  motor  decussation  a  distinct  collec- 
tion or  group  of  nerve-cells  exists,  one  on  each  side,  which  are 
located  in  the  middle  of  the  lateral  area,  adjacent  to  the  gray 
matter.     They  are  termed  the  nuclei  of  the  lateral  columns,  or 


itxn 


nX  t 


p    n.r.i.  r 


Fig.  73. — Section  of  the  Medulla  Oblongata  at  about  the  Middle  of  the 
Olivary  Body. — {After  Sckwalbe.) — [From  Qicain' s  "Anatomy.'''') 
f.l.a.  Anterior  median  fissure.  n.ar.  Nucleus  arciformis.  p.  Pyramid.  XII.  Bundle  of 
hypoglossal  nerve  emerging  from  the  surface  ;  at  3  it  is  seen  coursing  between  the  pyramid 
and  the  olivary  nucleus,  0.  f.a.e.  External  arciform  fibers,  n.l.  Nucleus  lateralis,  a. 
Arciform  fibers  passing  tovs^ard  restiform  body  partly  through  the  substantia  gelatinosa,  ^. , 
partly  superficial  to  the  ascending  root  of  the  fifth  nerve,  a.  V.  X.  Bundle  of  vagus  root, 
emerging,  f.r.  Formatio  reticularis.  C.r.  Corpus  restiforme,  beginning  to  be  formed, 
chiefly  by  arciform  fibers,  superficial  and  deep.  n.c.  Nucleus  cuneatus.  n.g.  Nucleus 
gracilis,  t.  Attachment  of  the  ligula.  f.s.  Funiculus  solitarius.  n.X.,n.X' .  Two  parts 
of  the  vagus  nucleus.  n.XII.  Hypoglossal  nucleus,  n.t.  Nucleus  of  the  funiculus  teres. 
n.am.  Nucleus  ambiguus.  r.  Raphe.  A.  Continuation  of  anterior  column  of  cord.  0'., 
0" .   Accessory  olivary  nuclei,     p.o.l.   Pedunculus  olivge. 


the  lateral  nuclei.  These  collections  of  nerve-cells  are  composed 
in  part  of  cell  groups  from  the  anterior  horns,  with  the  addition 
of  special  deposits  of  nerve-cells  found  in  this  area.  The  direct 
cerebellar  tracts,  or  columns  of  Flechsig,  occupy  the  same  rela- 
tive position  in  the  lateral  periphery  of  the  medulla  as  in  the 
spinal  cord,  being  situated  in  front  of  the  crescentic  bundle  of 


144  CENTRAL  NERVOUS  SYSTEM. 

fibers,  the  descending  root  of  tlie  fifth  nerve.  Here  also  the 
posterior  cohimns  continue  to  diverge,  the  central  canal  and 
o^rav  matter  broaden  out,  and,  after  trending^  backward,  the 
canal  opens  into  the  fourth  ventricle,  thus  exposing  the  central 
gray  matter  of  the  medulla  as  part  of  the  fioor  of  that  ventricle. 
Most  of  the  fibers  of  the  posterior  columns  have  ended  in 
their  respective  nuclei — namely,  in  an  inner,  club-shaped  mass 
next  to  the  median  line,  the  nucleus  of  the  column  of  Goll,  or 
nucleus  gracilis,  and  an  outer  broad  swelling,  the  nucleus  of  the 
column  of  Burdach,  or  nucleus  cuneatus.  Both  gray  masses 
contain  multipolar  nerve-cells,  about  which  the  fibers  of  the 
columns,  or  funiculi  graciles  and  cuneati,  end.  From  the  cells 
of  these  two  nuclei  new  axones  stream  out,  formine  bundles  of 
curved  fibers, — the  so-called  internal  arcuate  fibers, — which  pass 
anteriorly  through  the  gray  matter,  decussate  in  the  raphe  w^ith 
those  coming  from  the  opposite  side,  and  become  located  just 
posterior  to  the  anterior  pyramids,  between  the  olivary  bodies, 
whence  they  assume  a  longitudinal  course.  Edinger  has  proved 
by  embryologic  studies  that  many  of  these  fibers  surround  and 
pass  through  the  olivary  bodies  without  becoming  connected 
with  their  nerve-cells,  and  locate  themselves  in  the  above- 
described  area.  To  these  bundles  of  fibers  of  each  side  the 
name  mesial  fillet  or  lemniscus  has  been  given,  and  the  decus- 
sation has  been  called  the  sensory  decussation,  or  the  posterior 
pyramidal  decussation,  and  from  its  position  between  the  olivary 
bodies  it  is  often  called  the  interolivary  decussation.  This 
system  of  fibers — the  fillet  or  lemniscus — forms  a  long  tract, 
which  terminates  in  the  sensory  area  of  the  cerebral  cortex. 

The  higher  the  sections  of  the  medulla,  the  smaller  the  poste- 
rior nuclei  become,  because  nearly  all  their  fibers  are  lost  in  the 
arciform  fibers  of  the  fillet,  their  place  being  gradually  usurped 
by  the  appearance  of  the  broad  rope-like  bands, — the  restiform 
bodies,  or  the  inferior  cerebellar  peduncles, — which  at  this  level 
have  attained  considerable  size. 

The  head  of  each  posterior  horn  is  severed  from  its  narrow 
cervix  by  the  internal  arcuate  fibers  and  by  fibers  of  the  lateral 
area  passing  into  the  formatio  reticularis.  The  cervix  is  finally 
lost  in  this  latter  structure. 


Fig.  74. — Section  of  Medulla  Oblongata  at  Level  of  Sensory  Crossway. 
Weigert-Pal  preparation. 
a.  Anterior  pyramid  or  motor  tract,  b.  Inferior  olivary  body.  c.  Restiform  body  or  inferior 
cerebellar  peduncle,  d.  Internal  arcuate  fibers  from  nuclei  of  columns  of  Burdach  and 
Goll  passing  ventrally  to  decussate  between  the  olivary  bodies  (sensory  decussation),  e. 
Postero-external  arcuate  fibers.  /  Nucleus  of  column  of  Burdach.  g.  Nucleus  of  column 
of  Goll.  h.  Fourth  ventricle,  i.  Hypoglossal  nerve-roots,  j.  Raphe,  k.  Interolivary 
bundle,  median  fillet,  or  lemniscus. 

10  145 


I4<> 


CENTRAL   NKKVOUS  SVSTKM. 


Owino-  to  these  two  decussations,  the  fibers  of  the  <rround 
bundles  of  the  anterior  columns  are  displaced  dorsally,  so  that 
in  cross-sections  a  little  farther  brainward  they  come  to  occupy 
a  position  in  the  posterior  part  of  the  formatio  reticularis  on 
each  side  of  the  raphe. 


THE  RAPHE. 

The  raphe,  or  median  septum,  is  the  middle  line  of  the  medulla 
seen  on  transverse  section.  It  extends  from  the  bottom  of  the 
anterior  fissure  to  the  gray  matter  of  the  Hoor  of  the  fourth 
ventricle.  Here  the  various  fine  nerve-fibers  decussate  with 
their  fellows  of  the  opposite  side.  They  consist  largely  of  the 
fibers  coming  from  the  nuclei  of  the  posterior  columns,  known 
as  the  internal  arcuate  fibers,  with  a  small  number  of  external 
arcuate  fibers  from  the  same  source  and  fibers  from  the  various 
cranial  nerve  nuclei.  Scattered  among  the  various  decussating 
fibers  of  the  raphe  exist  a  number  of  multipolar  nerve-cells 
belonging  to  the  formatio  reticularis  alba. 


THE  FORMATIO  RETICULARIS. 

As  its  name  implies,  this  is  a  reticulated  meshwork  of  hori- 
zontal, longitudinal,  and  oblique  fibers,  crossing  one  another  at 
various  angles  and  having  interspersed  between  them  many 
multipolar  nerve-cells,  which  cells  collectively  are  called  the 
nucleus  reticularis  tegmenti  (Bechterew).  These  cells  of  the 
formatio  reticularis  are  doubtless  in  part  intrinsic  and  associative 
in  character,  combining  the  various  complex  acts  which  are  per- 
formed by  the  medulla  oblongata. 

This  formation  lies  between  the  olivary  bodies  and  the  nuclei 
of  the  posterior  columns,  and  is  bounded  laterally  by  the  direct 
cerebellar  tracts.  The  area  is  subdivided  into  two  regions,  a 
lateral  and  a  mesial.  The  former  borders  on  the  direct  cerebellar 
tract  of  the  medulla,  and  contains  a  large  number  of  ganglionic 
cells  derived  in  part  from  the  remains  of  the  anterior  horns. 
This  lateral  reeion  is  called  the  formatio  reticularis  grisea.  The 
mesial  area  is  located   between  the   raphe  and  the  hypoglossal 


Fig.  75.— Diagram  Indicating  the  Course  of  the  Motor  and  Sensory  Fibers 
OF  THE  Spinal  Cord  and  Medulla. 

,  a.  Motor  cells  of  the  cerebral  cortex,  b,  b.  Arborizations  of  the  fibers  of  the  sensory  tract 
in  the  cerebral  cortex,  c.  Nucleus  of  the  column  of  Burdach,  showing  terminal  arboriza- 
tions of  the  long  sensory  fibers  of  the  cord.  d.  Nucleus  of  the  column  of  Goll,  showing 
terminal  arborizations  of  the  long  sensory  fibers  of  the  cord.  e.  Section  of  the  medulla, 
showing  sensory  decussation.  /.  Section  of  medulla,  showing  motor  or  pyramidal  decus- 
sation, g,  g.  Motorial  end  plates,  h.  Section  through  the  cervical  region  of  the  cord, 
showing  termination  in  the  anterior  horn  of  the  motor  fibers  of  the  direct  pyramidal  tract 
after  they  have  crossed  in  the  anterior  commissure ;  also  fiber  of  crossed  pyramidal  tract  end- 
ing about  anterior  horn  cell  of  same  side.  i,i.  Posterior  spinal  ganglia.  j,k.  Sensory  fibers 
of  short  course.  /.  Sensory  fibers  of  long  course,  terminating  in  medulla,  m,  in,  in.  Sen- 
sory end  organs,     n.   Section  through  lumbar  cord. 

147 


THE   MEDULLA  OBLONGATA,  OR   BULB.  149 

nerve-roots,  and  because  it  is  composed  mainly  of  nerve-fibers, 
with  only  a  few  cells,  this  area  is  called  the  formatio  reticularis 
alba. 

The  fibers  of  the  formatio  reticularis  are  arranged  as  follows  : 
First,  the  horizontal  fibers  belonoring-  to  the  fillet  or  lemniscus. 
Second,  those  fibers  which  have  come  from  the  anterior  ground 
bundles  of  the  spinal  cord  and  have  trended  backward  to  form  the 
posterior  longitudinal  bundles,  and  which  appear  on  transverse 
section  as  two  distinct  bundles  of  nerve-fibers,  more  or  less  tri- 
angular in  shape,  on  each  side  of  the  raphe,  just  below  the  floor 
of  the  ventricle,  and  continue  to  occupy  the  same  relative  position 
beneath  the  aqueduct  of  Sylvius  until  they  reach  the  neighborhood 
of  the  nucleus  of  the  oculomotor  or  third  pair  of  cranial  nerves, 
beneath  the  anterior  corpora  quadrigemina.  In  their  course  they 
give  off  collaterals  to  the  nuclei  of  several  of  the  cranial  nerves, 
especially  those  concerned  in  the  movement  of  the  eyeballs.  Some 
of  the  fibers  of  the  posterior  longitudinal  bundles  end  in  arbori- 
zations about  the  cells  of  the  formatio  reticularis  grisea  from  the 
upper  part  of  the  pons  Varolii  to  the  anterior  corpora  quadrigem- 
ina. These  collections  of  cells  in  the  formatio  reticularis  of  each 
side  have  been  called  by  Koelliker  the  nucleus  magjzocelhdaris 
diffusus.  Third,  fibers  from  the  remains  of  the  lateral  columns 
which  pass  into  this  area.  These  in  part  probably  consist  of  the 
fibers  of  the  ground  bundles  of  the  lateral  columns.  These  fibers 
are  connected  with  the  cells  of  the  nucleus  reticularis  tegmenti, 
and  continue  brainward  to  the  region  of  the  posterior  corpora 
quadrigemina.  Fourth,  it  is  positive  that  Gowers'  anterolateral 
ascending  tract,  which  is  located  lateral  and  slightly  dorsal  to  the 
olivary  body,  passes  into  the  formatio  reticularis  grisea,  and 
thence  upward  to  the  pons,  where,  according  to  Hoche,  it  joins 
the  superior  cerebellar  peduncle  and  passes  to  the  cerebellum. 
Lastly,  are  found  the  before-mentioned  internal  arcuate  fibers, 
toofether  with  the  axones  and  collaterals  from  some  of  the 
cranial  nerves  and  those  from  the  cells  of  the  nucleus  reticularis 
tegmenti.  The  cells  of  the  formatio  reticularis  are  rather  large 
multipolar  cells  possessing  long,  thick,  branching  dendritic  pro- 
cesses with  strong  axis-cylinders,  which  pursue  different  courses. 
Their  common  course  is  inward  to  the  raphe,  where  they  decus- 


ISO 


CENTRAL  NERVOUS  SYSTEM. 


sate  and  pass  into  the  ventral  or  dorsal  parts  ot  the  formalio 
reticularis.  After  a  short  course  they  become  longitudinal  and 
give  off  numerous  collaterals,  which  often  bifurcate,  one  branch 


Fig.    76. — Section   through   Furmatio   Reticularis    ok    the    Medulla   Oblongata. 

Method  of  Weigert-Pal. 


passing  upward,  the  other  downward,  both  branches  probably 
ending  by  arborizing  about  the  cells  of  the  formatio  reticularis 
at  higher  and  lower  levels. 

Sections  at  this  level — that  is,  at  the  sensory  decussation — show 


THE  MEDULLA  OBLONGATA,  OR   BULB.  151 

the  interposition  of  several  of  the  cranial  nerve  nuclei — namely, 
the  twelfth,  or  hypoglossal,  the  ninth,  or  glossopharyngeal,  and 
the  tenth,  or  pneumogastric. 

The  nuclei  of  origin  of  the  twelfth  pair  are  found  on  each 
side  of  the  median  line,  beneath  the  floor  of  the  fourth  ventricle 
and  close  to  the  aforesaid  spinal  canal,  and  consist  of  large 
groups  of  multipolar  nerve-cells,  which  vary  from  25  to  70  fj. 
in  diameter.  Their  protoplasmic  processes,  or  dendrites,  are 
very  numerous,  and  pursue  a  rather  long  course.     According  to 


«*»•■•■> 


-"■**  jm " 


€f  .. 


''"^.^ 


Fig.  77. — MicROPHOTOGRAPH   FROM   A   Seven-months'    Human   Fetus   of   Section  of 
FoRMATio  Reticularis  Grisea.     The  cells  with  their  decussating  axones  are  seen. 

Van  Gehuchten,  many  of  the  dendrites  cross  the  median  line  and 
ramify  about  the  hypoglossal  nerve-cells  of  the  opposite  side, 
forming  a  protoplasmic  commissure.  The  axis-cyhnder  pro- 
cesses pass  in  slight  curves  ventrall}^  and  emerge  from  the 
medulla,  between  the  olivary  bodies  and  the  pyramids,  in  the 
anterolateral  groove.  Some  of  the  axones,  however,  frequently 
pass  through  the  mesial  portion  of  the  olivary  bodies  and 
between  the  fibers  of  the  anterior  pyramids,  having  their  point 
of  exit  in  a  slight  sulcus  on  the  ventral  aspect  of  the  pyramid  of 


152  CENTRAL  NERVOUS  SYSTEM. 

each  side.  Tliese  axis-cylinders,  or  root-fibers,  from  the  hypo- 
glossal nuclei  form  a  sharp  boundary-line  between  the  formatio 
reticularis  alba  and  grisea.  The  group  of  cells  from  which  these 
nerve-fibers  arise  corresponds  to  the  cells  which,  in  the  spinal 
cord,  are  located  at  the  base  of  the  anterior  horns.  But  owing 
to  the  previously  described  changes,  they  first  occupy  a  position 
ventrolateral  to  the  spinal  canal,  and  when  the  canal  opens  into 
the  fourth  ventricle,  they  come  to  lie  on  the  lloor  of  the  ventricle, 
on  each  side  of  the  median  line.  This  group  of  nerve-cells, 
on  transverse  section,  occupies  a  somewhat  triangular  field,  just 
beneath  the  ependyma  of  the  fourth  ventricle  on  each  side  of 
the  raphe  (Fig.  78). 

\^entral  to  the  chief  nucleus  of  the  hypoglossal  nerve  exists, 
in  the  formatio  reticularis,  slight  groups  of  small  multipolar 
nerve-cells,  which  surround  the  root-fibers  of  the  hypoglossal 
nerve.  These  collections  of  cells  form  the  hypoglossal  nucleus 
of  Roller. 

It  is  highly  improbable,  at  least  in  man,  that  the  axones  from 
these  small  cells  take  any  share  in  the  formation  of  the  root- 
fibers  of  the  hypoglossal  nerve. 


CONNECTIONS  OF  THE  HYPOGLOSSAL  NUCLEL 

Surrounding  this  nucleus,  and  passing  between  its  nerve- 
cells,  exist  large  numbers  of  very  fine,  and  also  coarse,  medul- 
lated  nerve-fibers,  which  fibers  give  to  this  nucleus  the  appear- 
ance of  a  stratum  zonale. 

These  fibers  arborize  about  the  nerve-cells  of  the  hypoglossal 
nucleus,  and  probably  form  the  means  of  connection  of  this 
nucleus  with  the  rest  of  the  nervous  svstem.  Their  source  is  as 
follows : 

1.  Fibers  from  the  motor  tract  (central  motor  tract  of  the 
hypoglossal  nerve),  which  occupy  the  middle  part  of  the 
motor  tract  and,  becoming  longfitudinal  at  the  level  of  this 
nucleus,  pass  diagonally,  and  crossing  in  the  raphe,  terminate 
about  the  hypoglossal  nerve-cells  of  the  opposite  side. 

2.  Fibers  enter  this  nucleus  from  the  posterior  longitudinal 
bundle. 


-^/■.i.\ 


1  'l 


Fig.  78. — Tran'sverse  Section  through  the  Hypoglossal  Nucleus.     Method  of 

Weigert-Pal. 


153 


THE   MEDULLA  OBLONGATA,  OR   BULB.  155 

3.  Collaterals  from  the  sensory  end  nuclei  ot  the  vagus, 
glossopharyngeal,  and  trigeminal  nerves  terminate  about  the 
cells  of  this  nucleus. 

4.  Large  numbers  of  radial  coursing  fibers,  which  appear 
to  come  from  the  olivary  bodies,  but  may  in  part  be  motor 
fibers  from   the  pyramidal  tract,  enter  this   nucleus  (Koelliker). 

5.  The  hypoglossal  nuclei  are  united  with  each  other  by  com- 
missural fibers  which  cross  in  the  raphe. 


THE  A^\GUS  AND  GLOSSOPHARYNGEAL  NERVES. 

The  vagus  and  glossopharyngeal  are  mixed  motor  and 
sensory  nerves,  and  are  connected  in  the  medulla  through  three 
nuclei.  The  motor  nerve-root  of  each  of  these  nerves  consists 
of  the  axones  from  the  cells  of  the  nucleus  ambiguus.  The  com- 
bined sensory  nerve-roots  represent  the  axones  from  the  mono- 
polar cells  of  the  jugular  and  petrosal  ganglia.  The  sensory 
axones,  on  entering  the  medulla,  do  not  immediately  bifurcate, 
but  pass  dorsally  between  the  descending  trigeminal  roots,  to 
terminate  after  bifurcating  among  the  cells  of  two  distinct  gray 
masses  located  in  the  dorsal  part  of  the  medulla.  On  approach- 
ing their  end  nuclei,  they  give  off  collaterals  which,  wdth  their 
axones,  arborize  about  the  cells  existinor  in  those  nuclei. 
There  are  thus  two  sensory  end  nuclei,  among  the  cells  of 
which  these  sensory  nerve  filaments  terminate.  The  first  of 
these  is  the  so-called  sensory  nucleus  of  origin,  and  is  located 
dorsolateral  to  the  nucleus  of  origin  of  the  hypoglossal  nerve, 
producing'  on  each  side  of  the  fioor  of  the  fourth  ventricle  the 
gray  prominence,  the  ala  cinerea,  or  trigonum  vagi,  which  ex- 
tends upward  to  the  fovea  inferior.  These  nuclei,  one  for  each 
side,  are  composed  of  small  spindle-  or  club-shaped  cells  about 
30  to  40  f.1  long  and  1 2  to  20  u  wide.  The  cell  groups  of  these 
nuclei  correspond  in  the  spinal  cord  to  cells  which  exist  at  the 
base  of  the  posterior  horns.  The  cells  of  the  upper  portion  of 
these  nuclei  are  connected  with  the  sensory  axones  of  the  glosso- 
pharyngeal nerves,  while  the  cells  of  the  lower  part  of  them  are 
in  relation  with  the  axones  of  the  pneumogastric  nerves.  The 
second  end  nucleus  consists  of  axones,  collaterals,  and  nerve- 
cells,  and  is  called   the  vertical  nucleus  of  Ramon  y  Cajal,  the 


156 


CENTRAL  NERVOUS  SYSTEM. 


fasciculus  solitarius  of  Lenhossek,  or  the  combined  descending 
root  of  the  vagus  and  glossopharyngeal  nerves ;  also  called  the 
respiratory  bundle  (Meynert,  Gierke,  Krause^  This  combined 
descending    root  of   the  vagus  and  glossopharyngeal  nerve  is 


— .^/ 


IS^ld 


Fig.  79.— Medull.\  Oblongata  from  a  Human  Embryo  of  Eight  Months. — {After 

JCoel/iker.) 
P.  Anterior  pyramid  whose  fibers  are  not  meduUated.  O.  Olivary  and  accessory  olivary 
bodies.  OC.  Cerebello-olivary  tract.  PC.  Cerebellar  peduncle,  Pt.  Ponticulus  or 
ligulse.  IX,  X.  Glossopharyngeal  and  pneumogastric  nerve-roots.  A''.  Combined  sen- 
sory end  nuclei  for  vagus  and  glossopharyngeal  nerves.  Fs.  Fasciculus  solitarius  with  de- 
scending fibers.  Xin.  Motor  root-fibers  of  vagus  and  glossopharyngeal.  A'^.  Nucleus 
ambiguus.  V.  Descending  sensory  trigeminal  nerve.  Villa.  Descending  vestibular 
tract.  FIJ.  Posterior  longitudinal  bundle.  S.  Median.  S'^ .  Lateral  fillet  or  lemniscus. 
52.  Interolivary  bundle.  RC.  Direct  cerebellar  tract.  A'//.  Hypoglossal  nucleus  and 
root-fibers. 


located  in  the  formatio  reticularis  on  each  side,  a  little  ventro- 
lateral to  the  first  sensory  end  nucleus.  It  extends  brainward 
nearly  as  high  as  the  superior  end  of  the  inferior  olivar}^  body, 


THE   MEDULLA  OBLONGATA,  OR   BULB. 


157 


and  as  far  spinalward,  according-  to  Krause  and  Cajal,  as  the 
eighth  cervical  nerve,  there  being  located  near  the  base  of  each 
posterior  horn.  It  has  its  greatest  size  just  above  the  calamus 
scriptorius,  and  gradually  decreases  in  size  from  above  down- 
ward, and  trends  backward  and  inward.  According  to  Koelliker, 
the  fasciculi  become  lost  among  the  fibers  of  the  funiculi  cuneati, 
but  Cajal  states  that  farther  below  they  again  become  prominent 


Fig.  80. — Transverse  Section  through  the  Medulla  of  a  Mouse  at  the  Level  of 
THE  Commissural  Nucleus. — {After  Ramon  y  Cajal.) 

A.  Commissural  nucleus.  B.  Nucleus  of  the  hypoglossal.  C.  Crossing  of  the  fibers  of  median 
fillet  or  lemniscus.  D.  Transverse  section  of  solitary  fasciculus,  a.  Cells  of  the  com- 
missural nucleus.  b,  c.  End  fibers  of  the  pneumogastric  and  glossopharyngeal.  d. 
Decussation  of  collaterals  from  the  hypoglossal  nerve-cells,  g,  f.  Sensory  collaterals 
terminating  about  the  cells  of  the  hypoglossal  nucleus. 


near  the  base  of  the  posterior  horns.  These  fasciculi,  one  for 
each  side,  consist  of  fine  axones,  collaterals,  and  end  brushes, 
with,  in  several  places,  deposits  of  gray  matter,  which  gray  mat- 
ter is  usually  located  mesial  to  the  nerve  bundles.  In  their 
upward  course  the  fasciculi  solitarii,  deep  beneath  the  epen- 
dyma  of  the  fourth  ventricle,  approach  the  raphe,  and  the  gray 
masses  unite  into  an  oval,  somewhat  saddle-shaped  nucleus — the 


ISS  CKNTRAL   NERVOUS  SYSTEM. 

commissural  nucleus  of  Cajal.  According  to  this  observer,  the 
fibers  of  the  solitary  bundles  lie  in  the  lateral  portion  of  this 
nucleus.  About  three-quarters  of  them  pass  the  middle  line, 
decussate  with  their  fellows,  and  then  arborize  about  the  cells 
existing  in  the  opposite  side  of  this  nucleus.  The  cells  of  this 
nucleus  are  small,  oval,  spindle,  or  angular,  having  very  fine 
neuraxones,  w^iich  pass  anteriorly  across  the  raphe,  forming 
bundles  of  fibers  which  enter  the  lemniscus  or  fillet,  which  is 
probably  the  central  sensory  tract  for  these  nerves.  This  res- 
piratory bundle  may  associate,  through  collaterals,  the  nuclei 
controlling  the  various  respiratory  muscles  (Figs.  79  and  80). 

The  Motor  Nucleus  of  the  Vagus  and  GlossopJiaryngeal  Nerves. 
— The  motor  root-fibers  of  the  vagus  and  glossopharyngeal 
nerves  are  the  axones  from  collections  of  multipolar  cells 
located  in  the  posterolateral  portion  of  the  formatio  reticu- 
laris of  each  side  deep  beneath  the  floor  of  the  fourth  ven- 
tricle and  mesial  to  the  detached  posterior  horns.  These 
cells  form  on  each  side  a  distinct  nucleus,  somewhat  pear- 
shaped,  which  is  prolonged  upward  to  near  the  superior  end  of 
the  inferior  olive  and  downward  to  the  beginning  of  the  sensory 
crossway.  It  has  received  the  name  of  nucleus  ambiguus. 
The  axones  of  the  cells  from  the  upper  portion  of  this  nucleus 
go  to  form  the  motor  root-fibers  of  the  glossopharyngeal, 
while  those  of  the  lower  portion  form  the  root-fibers  of  the 
pneumogastric  and  accessory  portion  of  the  spinal  accessory 
nerve.  About  the  cells  of  this  nucleus  exist  fine  end  brushes, 
probably  in  part  collaterals,  from  the  descending  root  of  the 
trigeminal  nerve,  thus  establishing  a  connection  between  the  fifth 
nerve  and  the  motor  division  of  the  vagus  and  glossopharyn- 
p-eal  nerves.  Collaterals  also  from  the  formatio  reticularis  grisea 
arborize  about  the  cells  of  this  nucleus.  No  collaterals  have  as 
yet  been  discovered  connecting  the  sensory  nerve  filaments  of 
the  vagus  and  glossopharyngeal  with  their  motor  nerve-cells, 
although  it  is  highly  probable  that  such  a  connection  exists.  The 
axones  from  the  cells  of  these  nuclei  pass  dorsally  to  a  point 
near  the  sensory  end  nuclei ;  then  they  form  distinct  curves  and 
pass  anterolaterally  through  the  formatio  reticularis  and  along- 
side of   the  sensory  fibers  from    their  respective    ganglia.      In 


THE    MEDULLA  OBLONGATA,  OR   BULB.  159 

their  course  they  give  off  a  few  collaterals,  which  decussate  in 
the  raphe  with  their  fellows  of  the  opposite  side. 


THE  OLIVARY  BODIES. 

The  olivary  bodies,  one  on  each  side,  are  embedded  in  the 
lateral  part  of  the  medulla  just  behind  the  anterior  pyramids, 
from  which  they  are  separated  by  the  emerging  hypoglossal 
nerve-roots.  Posteriorly,  they  are  separated  from  the  restiform 
bodies   by  the    dorsolateral   groove  for  the  exit  of  the  spinal 


\     I"- 


/.^  -/ 


Fig.  81. — MiCROPHOTOGRAPH    SHOWING  MULTIPOLAR    CELLS  OF    INFERIOR    OLIVARY    BODY. 

accessory,  pneumogastric,  and  glossopharyngeal  nerves.  A 
short,  deep,  transverse  groove  exists  between  these  bodies  and 
the  pons  Varolii  above.  The  olivary  bodies  produce  externally 
two  large,  oval-shaped  elevations,  with  their  long  axes  arranged 
longitudinally.  Numerous  fibers  may  be  seen  passing  across 
them  to  join  the  restiform  bodies.  They  are  about  i6  or 
17  mm.  long,  and  consist  of  a  mass  of  white,  medullated 
nerve-fibers,  surrounded  by  a  capsule  of  gray  matter  which 
presents  a  wavy,  sinuous    outline.     This    capsule  is  closed  at 


i6o  CENTRAL  NERVOUS  SYSTEM. 

either  end,  but  presents  on  its  median  surface  an  opening- 
— the  hilum.  On  transverse  section  the  capsule  may  be  seen 
to  consist  of  two  blades  or  laminae  :  an  anterior  or  ventral, 
and  a  posterior  or  dorsal.  The  anterior  blade  is  shorter  and 
its  direction  almost  transverse,  while  the  dorsal  or  posterior 
lamina  is  longer,  and  has  an  oblique  direction,  backward  and 
inward.  The  laminae  are  perforated  on  all  sides  by  bundles  of 
fine,  medullated  nerve-fibers  ;  part  of  these  fibers  are  rearranged 
within,  pass  out  of  the  hilum,  decussating  in  the  raphe,  and  end 
in  arborizations  about  the  nerve-cells  of  the  opposite  olivary 
bod)-.  This  bundle  of  fibers  on  each  side  forms  a  system, — the 
cerebello-olivary  tract, — which  will  soon  be  described.  The 
remaining  fibers,  fibriae  arcuatae,  simply  pass  through  the  olivary 
bodies  entering  the  formatio  reticularis  g-risea ;  while  those 
which  pass  through  the  anterior  or  ventral  lamina  probably  are 
external  arcuate  fibers.  Microscopically,  the  olivary  bodies  are 
composed  of  a  neuroglia  network,  in  the  meshes  of  which 
exist  a  great  many  small  multipolar  cells,  which  are  roundish 
or  pear-shaped,  contain  a  yellowish  pigment,  and  are  from 
1 8  to  26  a  in  diameter.  Each  cell  has  from  three  to  five 
dendrites,  and  a  long,  fine  neuraxone,  the  destination  of 
which  is  unknown,  although  Koelliker  believes  that  it  passes 
into  the  lateral  columns,  and  ends  about  the  motor  cells  of  the 
cord.  Cajal  states  that  some  of  these  neuraxones  become  trans- 
verse, cross  the  median  line,  pass  through  the  opposite  olivary 
body,  and  enter  the  white  matter,  while  others  pass  out  of  the 
olivary  body  without  decussating  and  are  lost  among  the  anterior 
external  arcuate  fibers.  These  bodies,  in  addition,  contain  a  vast 
number  of  fine  nerve-fibers,  which  end  in  brush-like  expansions 
about  the  cells.  They  are  probably  arborizations  from  the 
neuraxones  of  the  cells  of  Purkinje,  from  which,  according  to 
Koelliker,  the  cerebello-olivary  tract  arises  (Fig.  82). 

In  addition  to  the  olivary  bodies,  two  other  gray  masses  exist, 
havinor  about  the  same  histologic  construction,  which,  because  of 
their  proximity  to  the  former,  are  called  accessory  olivary  bodies. 
They  are  divisible  into  a  median  or  inner  accessory  olivary 
body  and  a  dorsal  or  posterior  accessory  olivary  body  on  each 
side.     The  inner  one  is  located  in  the   lemniscus,  just  dorsal  to 


Fig.  82.— Hemisection  of  Medulla  to  Show  Olivary  Body.     Method  of  Weigert-Pal. 

a.  Median  accessory  olivary  body.  b.  Anterior  median  fissure,  c.  Anterior  pyramid,  d. 
Nucleus  arciformis.  e.  Olivary  body.  /.  Dorsal  accessory  olivary  body,  which  also  in- 
cludes gray  mass  at  the  extremity  of  the  dorsal  lamina  of  olivary  body.  g.  Cerebello-oli- 
vary  tract. 

II  .  161 


THE    MEDULLA  OBLONGATA,  OR    BULB.  i6j 

the  pyramids  and  ventrolateral  to  the  anterior  lamina  of  the 
olivary  body.  Because  of  their  relation  to  the  anterior  pyramids, 
they  are  sometimes  called  the  pyramidal  nuclei.  The  dorsal  or 
posterior  accessory  body  is  found  just  dorsal  to  the  inner  portion 
of  the  posterior  blade  of  the  olivary  body  of  each  side.  These 
accessory  bodies  are  traversed  by  the  internal  arcuate  fibers  ; 
usually,  however,  the  root-fibers  of  the  hypoglossal  nerves  pass 
between  them  and  the  main  olivary  bodies.  In  the  ventral  part 
of  each  pyramid  among  the  external  arcuate  fibers  exists  a  tri- 
angular-shaped mass  of  gray  matter  called  the  nucleus  arciformis. 


THE  CENTRAL  TEGMENTAL  TRACT  OF  BECHTEREW  AND 

FLECHSIG. 

The  central  tegmental  tract  consists  of  a  small  bundle  of 
fibers,  which  probably  take  their  origin  from  the  olivary  body  of 
the  same  side.  This  bundle  is  located  in  the  formatio  reticularis, 
dorsal  to  the  olivary  body,  which  position  it  retains  until  it 
reaches  the  level  of  the  lower  border  of  the  pons  Varolii,  where 
it  becomes  located  dorsal  to  the  corpus  trapezoides  in  the  space 
between  the  superior  olivary  body  and  the  lemniscus  ;  at  a 
higher  level  in  the  pons  it  occupies  a  position  in  the  central  part 
of  the  tegmentum,  hence  its  name.  Still  higher  up,  this  bundle 
of  fibers  passes  between  the  crossing  fibers  of  the  superior 
cerebellar  peduncle,  and  then  takes  a  position  lateral  to  the  pos- 
terior longitudinal  bundle,  and  terminates,  according  to  Bech- 
terew,  in  the  region  of  the  third  ventricle.  Flechsig  states,  how- 
ever, that  the  fibers  of  this  tract  continue  brainward  and  end  in 
the  globus  pallidus  of  the  lenticular  nucleus.  Helweg  asserts 
that  the  fibers  of  this  tract  pass  in  part  into  the  lenticular  loop 
and  in  part  into  the  posterior  commissure.* 

SECTION  THROUGH    THE  MIDDLE    OF   THE    OLIVARY  BODIES. 

Here  the  motor  and  sensory  decussations  are  completed  ;  the 
restiform  bodies  occupy  the  lateral  periphery  of  the  section,  and 

*  It  is  probable  that  the  olivary  tract  of  Bechterew  or  the  triangular  bundle  of  Helweg  and 
the  central  tegmental  tract  form  a  functionally  continuous  bundle  of  fibers  which  connect  the 
spinal  cord  and  olivary  body  with  the  mid-brain. 


i64  CKNTRAL  NERVOUS  SVSTKM. 

have  attained  considerable  size.  The  gray  matter  is  broadened  ; 
the  anterior  and  posterior  horns  still  exist,  severed  from  their 
connection  with  the  gray  matter.  The  olivary  bodies,  with 
their  accessory  nuclei,  are  seen  with  their  wealth  of  cells  and 
fibers. 

At  this  level  exists  another  system  or  tract,  consisting  of 
fibers  which  decussate  in  the  raphe  and  pass  into  the  opposite 
olivary  body;  it  is  known  as  the  cerebello-olivary  tract.  Take, 
for  example,  the  right  cerebello-olivary  tract:  Its  fibers  come, 
according  to  Koelliker,  from  the  cells  of  Purkinje,  in  the  cere- 
bellar cortex  of  the  same  side,  and  pass  downward  in  the  lateral 
portion  of  the  restiform  body  until  they  reach  the  medulla,  when 
they  move  inward,  and  occupy  the  middle  portion  of  the  resti- 
form body  ;  they  then  pass  to  the  neighborhood  of  the  right 
olivary  body  in  curves,  "arcuate  fibers,"  where  they  spread 
out  and  almost  completely  surround  that  body  ;  they  then  pass 
through  its  laminx  into  its  interior,  where  the  fibers  are  re- 
arranged, forming  a  compact  bundle,  which  passes  out  at  the 
hilum  ;  the  fibers  decussating  with  their  fellows  of  the  opposite 
side,  entering  the  hilum  of  the  opposite  olivary  body,  and  ending 
in  arborizations  about  the  cells  of  that  body.*  The  axones  of  the 
cells  of  the  olivary  bodies  then  pass  outward  into  the  lateral 
column,  where  they  curve  downward  and  inward  to  terminate 
about  the  motor  cells  in  the  anterior  cornu  of  the  left  side. 

The  fibers  which  compose  this  tract  degenerate  downward. 
This  fact  has  been  proved  by  experimental  destruction  of  a 
cerebellar  hemisphere  of  a  young  animal,  when  there  followed 
complete  atrophy  of  this  tract  and  of  the  opposite  olivary  body. 
The  same  condition  has  been  observed  in  man  after  extensive 
disease  of  a  cerebellar  hemisphere. 

The  restiform  bodies,  which  at  this  level  have  attained  a  laree 
size,  are  composed  of  the  following  systems  of  fibers  : 

First,  the  direct  cerebellar  tract,  which  has  passed  backward 
into  the  restiform  body  of  the  same  side  ;  it  terminates  in  the 
cortex  of  the  superior  worm  of  the  cerebellum. 


*  Bechterew,  on  the  contrary,  believes  that  the  niajf)rity  of  the  fibers  of  this  tract  come  from 
the  cells  in  the  corpus  dentatum,  only  a  few  coming  from  the  cerebellar  cortex. 


THE    MEDULLA  OBLONGATA,  OR    BULB. 


165 


Second,  a  few  fibers  pass  from  the  cells  of  the  nuclei  gra- 
ciles  et  cuneati  around  the  outer  posterior  surface  of  the 
medulla,  reaching  the  restiform  body  of  the  same  side.  They 
are  called  the  postero-external  arcuate  fibers. 

Third,  fibers  from  the  nuclei  of  the  posterior  columns,  which 
are  continuations  of  the  interolivary  tracts.  After  decussating, 
they  pass  around  the  external  surface  of  the  opposite  anterior 
pyramid  and  olivary  body  and  join  the  restiform  body  of  the 
opposite  side.     These  are  the  antero-external  arcuate  fibers. 

The  posterior  external  arcuate  fibers  come  from  the  posterior 


Fig.  83. — The  Cerebello-olivary  Tract. — {After  Edittger.) 


nuclei  of  the  same  side,  while  the  anterior  external  arcuate 
fibers  come  from  the  posterior  nuclei  of  the  opposite  side. 

The  majority  of  these  fibers  pass  to  the  cortex  of  the  superior 
worm  of  the  cerebellum.  A  few  probably  go  to  the  corpus 
dentatum. 

Fourth,  fibers  pass  to  the  restiform  body  from  the  lateral 
nucleus  of  the  same  side. 

Fifth,  the  descending  tracts  of  Marchi  and  Lowenthal.  They 
may  have  their  origin  in  the  cerebellar  cortex  and  pass  down- 
ward into  the  restiform  bodies  ;  thence  into  the  anterolateral 
areas  of  the  cord.  They  probably  end  in  the  median  gray  matter 
of  the  cord. 


i66  CENTRAL    NKRVOUS   SYSTEM. 

Sixtli,  the  direct  sensory  cerebellar  tract  passes  into  the  resti- 
form  body  and  thence  to  the  cerebellar  cortex,  thus  establishing 
a  connection  between  the  nucleus  vestibularis  of  the  auditory 
nerve  and  the  cerebellar  hemisphere. 

Seventh,  the  large  bundle  of  fibers  of  the  cerebello-olivary 
tracts  already  described. 


A  TRANSVERSE  SECTION  OF  THE   MEDULLA  NEAR  ITS 
JUNCTION   WITH  THE  PONS. 

The  restiform  bodies  here  are  very  large,  and  are  gradually 
passing  into  the  cerebellum.  The  olivary  bodies  are  greatly 
diminished  in  size.  The  crescentic  bundles  of  fibers  of  the  fifth 
pair  of  nerves  may  be  seen  internal  to  the  restiform  bodies. 
Dorsal  and  slightly  medianward  to  the  restiform  body,  lying 
between  it  and  the  dorsal  nucleus  of  the  auditory  nerve,  exists 
on  each  side  an  oblong  area  of  longitudinal  fibers,  known  as  the 
aciisticocerebellar  or  the  direct  sensory  cerebellar  tract.  This  tract 
extends  downward  as  far  as  the  posterior  columns  of  the  cord, 
and  contains  fibers  which  connect  the  cells  of  Deiter's  nucleus 
with  the  cerebellar  cortex.  According  to  Edinger,  this  tract 
comes  from  the  cerebellum,  and  is,  in  reality,  the  fasciculus  solita- 
rius,  or  the  combined  descending  vagoglossopharyngeal  root. 
Koelliker  believes  that  it  is  connected  with  the  sensory  nuclei 
of  the  trigeminal,  vagus,  and  glossopharyngeal  nerves  and  ter- 
minates in  the  posterior  columns.* 

Three  nerve  nuclei  occur  in  this  region — namely,  the  sixth  or 
abducens,  the  seventh  or  facial,  and  the  eighth  or  auditory. 

The  abducens  or  sixth  pair  of  cranial  nerves  represent  the 
axones  from  a  collection  of  multipolar  nerve-cells,  40  to  50  // 
in  diameter,  located  just  beneath  the  floor  of  the  fourth  ventricle, 
external  to  the  posterior  longitudinal  bundles  and  below  the 
striae  acousticse.  The  nucleus  of  each  side  is  inclosed  in  the 
loop  of  the  facial  nerve.  According  to  Obersteiner,  the  root- 
fibers  of  this  nerve  receive  an  accession  of  fibers  from  the  oppo- 
site nucleus,  they  having  crossed  in  the  raphe.     The  root-fibers 

*  Ferrier  and  Turner  believe  the  direct  sensory  cerebellar  tract  to  be  an  efferent  bundle  of 
fibers  from  the  middle  lobe  of  the  cerebellum  to  Deiter's  nucleus. 


THE   MEDULLA  OBLONGATA,  OR   BULB. 


167 


then  pass  anteriorly  through  the  gray  and  white  matter,  and 
emerge  in  a  depression  existing  at  the  junction  of  the  pons  with 
the  medulla,  just  external  to  the  fibers  of  the  anterior  pyramid. 
The  innermost  fibers  of  this  nerve  frequently  pierce  the  anterior 
pyramid ;  the  nerve  is  then  directed  upward  and  forward  upon 
the  anterior  surface  of  the  pons  Varolii. 

The  nuclei  of  the  abducens  are  connected  with  the  posterior 
longitudinal  bundles  by  fibers  which,  it  is  believed,  pass  to  the 


Fig.  84. — Tra-nsverse  Section  through   the   Pons  Varolii.      Illustrating  the  origin  of 
the  sixth  and  seventh  cranial  nerves. 

The  nucleus  of  the  seventh  is  not  shown,  but  its  fibers  can  be  seen,  a,  arching  over  the  nucleus 
of  the  sixth  nerve,  b.  Raphe,  c.  Fibers  of  the  abducens  nerve,  d.  Deep  transverse 
pontine  fibers,     e.  Pyramidal  tract,      f.   Superficial  transverse  pontine  fibers. 


opposite  oculomotor  nucleus,  thus  permitting  the  associative 
movements  of  the  eyeballs.  These  nuclei  are  also  connected  by 
fibers  with  the  superior  olivary  bodies.  (See  p.  176.)  These 
bodies  are  in  relation  with  fibers  from  the  auditory  nuclei,  and 
owing  to  the  connection  of  these  latter  nuclei  with  the  cerebellum, 
there  is  established  an  association  between  the  motor  nerves  of 
the  eyes,  the  auditory  nerves,  and  the  cerebellar  cortex.     This 


i6S  CENTRAL  NERVOUS  SYSTEM. 

association  may  be  of  great  service  in  enabling  us  to  judge  of 
our  position  in  space. 

The  facial  nerve  is  a  mixed  motor  and  sensory  nerve,  consist- 
ing of  a  large  motor  and  a  small  sensory  root.  The  sensory 
root  comes  from  the  cells  of  the  o^eniculate  oanorlion,  and  is 
called  the  nerve  of  Wrisberg,  while  the  motor  root  represents 
the  axones  from  a  nucleus  in  the  pons  at  its  junction  with  the 
medulla.  The  motor  nucleus  is  located  deep  in  the  lateral  por- 
tion of  the  formatio  reticularis,  is  about  four  millimeters  long,  and 
presents  on  transverse  section  a  roundish  or  slightly  oblong 
form.  It  consists  of  a  group  of  large,  mostly  pigmented,  multi- 
polar nerve-cells,  which  are  surrounded  by  a  fine  meshwork  of 
fibers.  This  nucleus  is  probably  the  upward  continuation  of 
the  nucleus  ambiguus,  which  at  a  lower  level  gave  origin  to  the 
motor  fibers  of  the  vagus  and  glossopharyngeal  nerves.  Some 
authors  claim  this  nucleus  to  be  the  upward  continuation  of  part 
of  the  cell  group  of  the  severed  anterior  horn.  The  axones  from 
the  cells  of  this  nucleus  pass  at  first  dorsomesially  to  reach  the 
floor  of  the  fourth  ventricle,  where  they  form  a  distinct  elevation 
— the  eminentia  teres,  or  the  tuberculum  nervi  facialis.  At  this 
point  the  fibers  are  located  just  external  to  the  posterior  longi- 
tudinal bundle  ;  they  then  make  a  sudden  bend  and  pass  ventro- 
laterally  between  the  facial  nucleus  and  the  sensory  trigeminal 
nerve-roots  to  their  point  of  emergence — the  upper  end  of  the 
medulla  at  its  junction  with  the  pons,  in  a  depression  between 
the  olivary  and  restiform  bodies.  Inclosed  in  the  loop  or  genu 
formed  by  the  two  curves  of  this  nerve  is  the  nucleus  of  the  sixth 
or  abducens  nerve.  Just  as  the  fibers  of  the  facial  are  about  to 
become  horizontal  beneath  the  ependyma  of  the  fourth  ventricle 
they  give  off  collaterals,  which  cross  the  median  line  and  end 
about  the  cells  of  the  facial  nucleus  of  the  opposite  side.  It  is 
a  well-known  fact  that  in  facial  paralysis  the  result  of  a  central 
lesion,  the  lower  branches  only  are  affected,  and  the  orbicularis 
palpebrarum  and  frontalis  muscles  remain  normal ;  it  is  possible, 
as  suggested  by  Mendel,  that  those  muscles  are  supplied  with 
fibers  that  join  the  facial  through  the  motor  oculi  nerve.  They 
probably  pass  in  the  posterior  longitudinal  bundle  and  join  the 
facial  at   its  genu.     The   nerve   of  Wrisberg,   or    the    sensory 


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THE    MEDULLA  OBLONGATA,  OR    BULB.  171 

division  of  the  facial,  represents  the  axone  from  the  cells  of  the 
geniculate  gang-lion  (P.  Martin).  These  axones  possess  both  a 
peripheral  and  a  central  division  ;  the  central  division  passes  into 
the  medulla  to  the  region  of  the  fasciculus  solitarius  or  the  com- 
bined descending  vagus  and  glossopharyngeal  roots.  The 
peripheral  fibers  join  the  facial,  and,  according  to  Duval,  are 
probably  those  which  go  to  form  the  chorda  tympani  nerve,  and 
are  concerned  with  the  special  sense  of  taste. 


CONNECTIONS  OF  THE  FACIAL  NERA^E. 

The  facial  nuclei  are  connected  with  the  motor  tracts  by  col- 
laterals which  pass  from  these  tracts  dorsally,  decussate  in  the 
raphe  near  the  bottom  of  the  ventral  fissure,  and  then  course 
dorsolaterally  to  end  about  the  cells  of  the  facial  nuclei. 

The  facial  nerve  is  also  connected  with  the  sensory  trigeminal 
nerve  by  four  or  five  bundles  of  fibers,  which  are  collaterals 
from  the  descending  trioreminal  nerve-roots. 

This  nucleus  is  indirectly  connected  with  the  cochlear  division 
of  the  auditory  nerve  by  fibers  from  the  corpus  trapezoides  and 
superior  olivary  body. 


THE  AUDITORY  xNERVE. 

The  auditory  nerve,  or  the  nerve  of  the  special  sense  of  hear- 
ing, possesses  two  roots,  which  differ  both  in  their  anatomic 
relation  and  physiologic  functions.  The  first,  which  is  called  the 
cochlear  nerve,  presides  over  the  function  of  hearing ;  the 
second  root,  or  vestibular  nerve,  is  concerned  in  the  maintenance 
of  equilibrium.  The  cochlear  nerve  is  also  termed  the  lateral, 
posterior,  or  dorsal  root ;  the  vestibular,  the  ventral,  anterior,  or 
mesial  root. 

The  cochlear  nerve  represents  the  axones  from  the  cells 
of  the  spiral  ganglion  located  in  the  bony  wall  of  the  cochlea 
which  forms  the  anterior  part  of  the  labyrinth.  The  periph- 
eral axones  from  the  cells  of  this  o-anelion  end  about  the 
ciliated  cells  of  the  oro-an  of  Corti  in  the  cochlear  duct.  The 
central  axones  as  they  exist  in    the  internal    auditory  meatus 


•7^ 


CENTRAL  NERVOUS  SYSTEM. 


resemble  in  their  position  the  posterior  root  of  a  spinal  nerve. 
The  cochlear  nerve  in  its  centripetal  course  then  enters  the 
lowermost  part  of  the  pons,  external  or  lateral  to  the  resti- 
form  body,  and,  without  decussating,  terminates  in  an  end 
nucleus — the  ventral  acoustic  nucleus. 

The  vestibular  nerve  represents  the  axones  from  a  swelling 
or  ganglion  in  the  auditory  meatus  called  the  vestibular  gan- 
glion, or  the  intumescentia  gangliformis  of  Scarpa.     The  per- 


FiG.  86. — Transverse  Section  tiikoucii  hie  Ijistal  Part  oe  the  Pons  of  an  Eight- 
months'  Human  Embryo. — {After  KoelUker.) 
P.   Superficial  pontine  fibers  (non-medullated).     Py.   Anterior  pyramid.       VIII'^.   Ventral  audi- 
,     tory  nucleus  from  which  the  medullated  fibers  of  the  corpus  trapezoides  arise.       VIII"^. 
■■■'  Dorsal    auditory  nucleus.      jVv.   Nervus    vestibuli.       V//^.    Emerging    facial    nerve-roots. 
y//.  Nucleus  of  the  facial  nerve.      F/.  Abducens  nerve.     L.  Lemniscus.     P/.  Posterior 
longitudinal  bundle.     P.arc.i.   Internal  arcuate  fibers.     Nc.   Cochlear  nerve.     Pc.  Cere- 
bellar peduncle.     Aa.   Descending  auditory  root.     7'gr.   Substantia  reticularis  grisea.      V. 
Descending  trigeminal  nerve-roots.       F^.   End  nucleus  of  trigeminal  nerve. 

ipheral  axones  are  distributed  to  the  fusiform  cells  of  the 
semicircular  canals.  The  central  axones  of  the  vestibular  nerve 
take  a  course  internal  to  the  ventral  acoustic  nucleus  and  resti- 
form  body,  being  located  between  the  latter  and  the  sensory 
bundle  of  the  fifth  nerve.  In  their  course  dorsally  they  bifur- 
cate, the  branches,  with  their  collaterals,  ending  about  the  cells 
of  Deiter's  nucleus  and  the  chief  auditory  nucleus.  The  cells 
of  both  spiral  and  vestibular  ganglia  are  bipolar. 


THE   MEDULLA  OBLONGATA,  OR   BULB. 


173 


Both  divisions  of  the  auditory  nerve  are  connected  in  the 
medulla  and  pons  with  three  end  nuclei :  first,  the  anterior,  ven- 
tral, or  lateral  acoustic  nucleus ;  second,  the  dorsomesial,  or 
chief  auditory  nucleus  ;  and  third,  the  dorsolateral,  or  nucleus  of 
Deiter.  The  anterior  nucleus  is  an  oval  collection  of  nerve-cells 
wedged  in  between  the  cerebellum  in  front  and  the  restiform 
body  behind.      It  produces  on  the  outer  surface  of  the  medulla 


Fig.  87. — MiCROPHOTOGRAPH  Showing  Cells  of  Ventral  Auditory  Nucleus.     Method 

of  Golgi. 

an  enlargement  known  as  the  tuberculum  acousticum.  The 
anteroposterior  diameter  of  this  nucleus  is  about  three  milli- 
meters, and  its  transverse  about  two  millimeters.  It  consists  in 
man  of  two  portions — dorsal  and  ventral.  The  ventral  portion, 
often  called  the  nucleus  accessorius,  consists  of  many  rather 
small,  roundish  cells,  25  to  35  f.i  in  size,  which  resemble 
closely  those  of  the  posterior  spinal  ganglia.  They  are  sur- 
rounded   by  a    great    number    of  fine  nerve    terminals.      The 


174 


CENTRAL  NERVUL'S  SYSTEM. 


dorsal  portion,  or  tiiberculum  acousticiim,  wliich  is  located 
between  the  cerebellum  and  the  pons,  consists  of  two  forms  of 
cells — small,  round  ones,  and  large,  somewhat  cylindric-shaped 
cells  ;  these  are  fewer  in  number  than  those  of  the  anterior  por- 
tion. The  dorsomesial,  or  chief  nucleus  of  the  auditory,  or 
nucleus  vestibularis,  occupies  a  large  triangular  area  just  beneath 
the  floor  of  the  fourth  ventricle,  external  to  the  combined  sensory 


F.r/i. 


D        I'lin 


^^W'^'^^^S^^^^'^S.   '■^S- 


*^:%^k 


Fig.  88. — Dorsal  Part  of  a  Transverse  Section  of  the  Medilla  Ohlong.via  from 
A  Human  Emuryo  of  Six  lA.oy>iw%.— [After  Koelliker.) 

Fl.  Posterior  longitudinal  bundle.  \'l.  Abducens  nerve.  VI  ^.  Nucleus  of  abducens.  VII. 
Facial  nucleus.  Vll^.  Ascending  axones  from  cells  of  facial  nucleus.  VII -.  Knee  of 
facial  nerve.  VII  ^.  Emerging  facial  fibers.  7)-.  Corpus  trapezoides.  Oo.  Superior 
olivary  body.  Xv.  Vestibular  nerve.  F///.  Ventral  auditory  nucleus.  VIII^.  Descend- 
ing vestibular  root.  D.  Nucleus  of  Deiter.  1\  Sensory  trigeminal  nerve-root.  /•'.;//. 
Fovea  of  the  fourth  ventricle. 


nucleus  of  the  vagus  and  glossopharyngeal  nerves  and  postero- 
internal to  the  restiform  body.  This  nucleus  consists  mainly  of 
small  multipolar  nerve-cells,  about  20  a  in  diameter.  The 
dorsolateral,  or  large-celled  nucleus  of  Deiter,  is  located  poste- 
rior to  the  restiform  body  and  dorsolateral  to  the  chief  auditory 
nucleus,  embedded  in  the  field  of  fibers  which  form  the  direct 
sensory  cerebellar  tract.  This  nucleus  may  easily  be  distin- 
euished  from   the  former  nucleus  bv  the  larcre  size  of  its  cells, 


THE    MEDULLA  OBLONGATA,  OR    BULB.  175 

which  are  multipolar,  and  are  from  40  to  100  u  in  diameter.  It 
increases  in  size  from  below  upward.  At  the  point  where  the 
fibers  of  the  restiform  body  pass  into  the  cerebellum  it  is  more 
dorsally  located,  and  has  its  greatest  size.  This  part  of  the 
nucleus  is  called  the  nucleus  of  Bechterew,  or  nucleus  vestibu- 
laris of  Flechsig. 

The  fine  fibers  of  which  the  cochlear  nerve  is  composed  are 
related  to  the  cells  of  both  divisions  of  the  ventral  or  lateral 
auditory  nucleus.  On  entering  the  nucleus  they  divide  Y-shape, 
one  division  passing  upward,  the  other  downward,  each  division 
giving  off  several  collaterals  ;  these  divisions,  with  their  collater- 
als, further  subdivide  into  fine  plexuses  about  the  cells  of  this 
nucleus.  The  rather  coarse  fibers  of  the  vestibular  nerve  pass 
dorsolaterally  through  the  medulla,  internal  to  the  ventral  audi- 
tory nucleus  and  restiform  body,  and  when  they  approach  their 
end  nuclei,  the  chief  auditory  nucleus,  and  the  nucleus  of  Deiter, 
they  divide  Y-shaped,  giving  off  at  the  same  time  numerous  col- 
laterals, one  division  passing  brainward,  the  other  spinalward. 
The  former  ends  about  the  cells  of  these  two  end  nuclei,  while 
the  latter  branches,  forming  the  so-called  descending  division  of 
the  vestibular  nerve.  These  latter  fibers,  with  their  collaterals, 
end  in  fine  end  brushes  about  a  group  of  cells  which  continue 
downward  on  both  sides  as  far  as  the  cuneate  nuclei.  Some  of 
the  cells  of  this  group  are  large,  while  others  are  small. 
Monakow  and  Koelliker  believe  these  cell  groups  to  be  a 
continuation  downward  of  the  nuclei  of.  Deiter.  They  may  be 
considered  as  the  descendino-  nuclei  of  the  vestibular  nerves. 

Connections  of  the  Auditory  Nerve. — The  axones  from  the 
cells  of  the  accessory  division  of  the  ventral  auditory  nucleus  pro- 
ceed toward  the  raphe,  producing  transverse  bundles  of  fibers 
which  are  located  just  posterior  to  the  anterior  pyramids  called 
the  corpora  trapezoidea.  Among  the  fibers  of  each  corpus  trape- 
zoideum  exist  numbers  of  large,  spindle-shaped,  multipolar  nerve- 
cells,  whose  axones  pass  anteriorly,  and  then  bend  at  an  angle 
and  assist  in  the  formation  of  the  corpus  trapezoideum  by  forming 
transverse  fibers.  The  fibers  pass  in  part  into  the  superior  olivary 
body  of  the  same  side,  while  the  remainder  decussate  in  the  raphe 
and  pass  to  the  superior  olivary  body  of  the  opposite  side. 


176  CENTRAL  NERVOUS  SYSTEM. 

IHt:  SLPKRIOR  OLIVARY  BODIES. 

These  are  cylinclric  masses  of  gray  matter,  consisting 
of  neuroci^lia  fibers,  fine  nerve  terminations,  and  numerous 
pear-  or  spindle-shaped  cells,  which  possess  a  single  axis- 
cylinder  and  numerous  dendritic  branches.  These  cells  begin 
at  about  the  level  where  the  nuclei  of  the  facial  nerves  are  first 
observed,  and  are  located  anterior  and  slightly  internal  to  them. 
They  are  surrounded  by  the  fibers  of  the  corpora  trapezoidea, 
which  fibers  end  about  their  nerve-cells.  A  few  axones  of  the 
cells  of  the  superior  olivary  bodies  pass  dorsally  to  end  about 
the  nuclei  of  the  abducens  nerve.  The  majority  of  the  axones 
of  the  superior  olivary  bodies  pass  dorsolaterally,  decussate 
in  the  raphe,  and  form  the  lateral  fillet  of  the  opposite  side. 
This  fact  seems  to  be  proved  by  the  experiment  of  Baginski, 
which  showed  that  after  the  destruction  of  the  cochlea  in  a 
young  animal  there  followed  an  atrophy  of  the  ventral  auditory 
nucleus,  the  corpus  trapezoideum,  the  superior  olivary  body, 
all  of  the  same  side,  and  of  the  lateral  fillet  of  the  opposite  side. 
Most  of  the  axones  from  the  cells  of  the  tuberculum  acousticum 
and  a  few  from  the  nucleus  accessorius  pass  around  the  resti- 
form  body  of  each  side,  then  proceed  just  beneath  the  ependyma 
of  the  ventricle,  where  they  are  known  as  the  strict  acousticse, 
until  they  approach  the  raphe  ;  they  then  pass  ventrolaterally, 
decussate  in  the  raphe,  and  enter  the  lateral  fillet  of  the  opposite 
side.  A  few  fibers  do  not  decussate,  but  go  to  the  fillet  of  the 
same  side.  Monakow  found  that  the  destruction  of  the  lateral 
fillet  close  to  the  corpus  quadrigeminum  was  followed  by  an 
atrophy  of  the  striae  acousticae  of  the  opposite  side.  The  nucleus 
of  the  lateral  fillet  or  lemniscus  is  the  upward  continuation  of 
the  cells  of  the  superior  olive  of  each  side.  This  group  of  cells 
continues  from  the  upper  end  of  the  superior  olive  to  near  the 
point  where  the  fillet  fibers  join  the  posterior  corpus  quadrige- 
minum. 

CONNECTIONS  OF   THE  VESTIBULAR  NERVE. 

I.  IVith  the  Cerebellum. — The  nucleus  of  Deiter  is  connected 
with  the  cerebellum,  first,  by  a  large  bundle  of  fibers — the  acous- 


THE    MEDULLA  OBLONGATA,  OR    BULB.  177 

tico-cerebellar  tract;  also  called  the  direct  sensory  cerebellar 
tract  (Edinger).  Much  doubt  still  exists  in  regard  to  the  source 
of  the  fibers  of  which  this  tract  is  composed.  Some  observers 
(Russel,  Ferrier,  and  Turner)  believe  it  to  be  an  efferent  tract 
connecting  the  middle  lobe  of  the  cerebellum  with  Deiter's 
nucleus,  while  Koelliker  believes,  from  embryologic  study,  that 
the  tract  consists  chiefly  of  axones  from  the  cells  of  Deiter's 
nucleus,  a  few  coming  from  the  cells  of  the  chief  auditory  nucleus. 
The  fibers  passing  into  the  middle  portion  of  the  restiform  body 
and  proceeding  to  the  region  of  the  roof  nuclei  of  the  cerebellum, 
between  which  nuclei  they  decussate  with  their  fellows  from  the 
opposite  side,  to  end  in  the  opposite  roof  nucleus. 

2.  With  the  Lateral  Fillet. — The  second  connection  is  by 
fibers  from  the  nuclei  of  Deiter  and  the  chief  nuclei,  which 
course  ventrolaterally  into  the  formatio  reticularis,  cross  over 
in  the  raphe,  and  pass  to  the  dorsal  surfaces  of  the  superior 
olivary  bodies,  where  they  assist  in  the  formation  of  the  lateral 
fillet  of  each  side. 

3.  With  the  Internal  or  Mesial  Fillet. — The  third  connection 
is  by  axones  proceeding  from  the  cells  of  Deiter's  nucleus  and 
coursing  ventromesially  between  the  root-fibers  of  the  vestib- 
ular branch  and  the  mesial  nerve,  and  turn  upward,  probably 
entering  the  internal  fillet  or  lemniscus. 

4.  With  the  Nuclei  of  the  Sixth  Nerve. — The  fourth  connec- 
tion is  formed  by  fibers  from  both  end  nuclei  of  the  vestibular 
nerve  to  the  abducens  nuclei. 

'  5.  With  the  Olivary  Body  and  the  Lateral  Cohtmn  of  the 
Same  Side. — The  fifth  connection  is  by  the  descending  vestibular 
olivary  tract  and  the  descending  vestibular  spinal  tract  (Van 
Gieson).  The  vestibular  olivary  tract  passes  ventromesially 
through  the  lateral  field  of  the  formatio  reticularis  and  ends  in 
the  olivary  body  of  the  same  side.  The  descending  vestibular 
spinal  tract  passes  through  the  periphery  of  the  lateral  field  of 
the  formatio  reticularis  and  descends  in  the  lateral  column  of 
the  spinal  cord.     Its  ultimate  distribution  is  unknown. 


178 


CENTRAL  NERVOUS  SYSTEM. 


THE  PONS  VAROLII. 

The  pons  lies  between  the  brain  stem,  or  crura  cerebri,  above, 
the  medulla  below,  and  the  cerebellum  behind.  It  serves  to 
connect  the  cerebrum  with  the  cerebellum  and  the  cerebellar 
hemispheres  with  each  other  by  means  of  broad,  transverse 
bundles   of  fibers.      It   permits   most  of  the   long  tracts  of  the 

a 


Fig. 


Method  of 


). — Transversa  Section  through  Upper   Part  of  Pons  Varolii. 

Weigert-Pal. 

a.  Aqueduct  of  Sylvius.  />.  Posterior  corpus  quadrigeminum.  c.  Posterior  longitudinal  bundle. 
d.  Beginning  decussation  of  superior  cerebellar  peduncles,  e.  Lateral  fillet  or  lemniscus. 
/.  Median  fillet  or  lemniscus.  //,  //.  Deep  transverse  pontine  fibers.  ^,  g.  Fasciculi  of 
pyramidal  tract.     ?.   Superficial  transverse  pontine  fibers. 

medulla  to  continue  brainward  without  any  special  change  ot 
relative  position.  It  contains  a  few  special  gray  deposits,  whose 
cells  give  origin  to  the  auditory,  facial,  abducens,  and  trigeminal 
nerves.  The  auditory  and  facial  nerves  come  out  lateral  to  the 
abducens  at  the  junction  of  the  pons  with  the  medulla.  The 
abducens    comes    out   at    the   junction    of    the    pons    with    the 


THE   MEDULLA   OBLONGATA,  OR   BULB.  179 

medulla,  close  to  the  median  surface  of  the  pons  in  the  upper 
end  of  the  ventrolateral  groove.  The  fifth  pair,  or  trigeminal 
nerves,  emerge  from  the  lateral  part  of  the  ventral  surface  of  the 
pons,  just  above  its  central  portion.  The  anterior  surface  of  the 
pons  is  convex,  and  rests  in  the  sphenobasilar  groove.  This 
surface  is  contracted  laterally,  owing  to  the  convergence  of  the 
broad  bundles  of  transversely  arranged  fibers,  which  fibers  form 
a  commissural-like  arch  between  the  hemispheres  of  the  cere- 
bellum. The  above  fibers  form  the  middle  peduncles  of  the 
cerebellum.  They  are  divided  into  a  superficial  and  a  deep  set 
by  the  passage  through  them  of  the  anterior  pyramids,  or  great 
motor  tracts.  Along  the  middle  of  the  ventral  surface,  running 
from  before  backward,  is  a  groove  in  which  the  basilar  artery 
rests.  The  dorsal  surface  forms  the  upper  half  of  the  floor  of 
the  fourth  ventricle.  Its  middle  part  is  somewhat  flattened, 
while  its  sides  are  elevated,  due  to  two  broad  bands  of  white 
fibers, — the  superior  peduncles  of  the  cerebellum, — which  have 
come  from  the  neighborhood  of  the  corpora  quadrigemina. 
They  form  the  upper  and  outer  boundary  of  the  fourth  ventricle, 
which  at  this  point  is  gradually  narrowing  into  the  aqueduct  of 
Sylvius,  which  serves  to  connect  the  fourth  ventricle  with  the 
ventricle  above,  or  the  third  ventricle.  The  superior  portion  of 
the  pons  arches  over  the  crura  cerebri. 


A  TRANSVERSE  SECTION  OF  THE  PONS. 

The  pyramids,  which  occupy  a  position  anteriorly,  are  no  longer 
free,  as  they  were  in  the  medulla,  being  concealed  between  the 
superficial  and  deep  transverse  fibers,  but  they  still  remain  as 
two  distinct  bundles  of  fibers,  while  above  the  middle  of  the  pons 
they  are  separated  into  a  number  of  fasciculi.  Between  the  trans- 
verse fibers  of  the  pons  exists,  on  each  side,  a  large  number  of  small, 
multipolar  nerve-cells,  forming  groups  called  the  nucleus  pontis. 
According  to  Cajal,  the  fibers  of  the  corticocerebellar  tracts  end 
in  brush-like  expansions  about  these  cells,  and  are  further  con- 
tinued by  the  axones  of  these  cells,  which  pass  as  transverse 
fibers  to  the  cortex  of  the  cerebellum.  Koelliker  believes  that 
many  of  these  transverse  fibers  conduct  impulses  centrifugally, 
and  are  the  axones  from   the   cells  of  Purkinje,  which   end  in 


l8o  CENTRAL  NERVOUS  SYSTEM. 

arborizations  about  the  cells  of  the  nuclei  pontis  of  the  same 
and  opposite  side.  Posterior  to  the  transverse  fibers  is  the 
formatio  reticularis,  which  is  an  upward  continuation  of  the 
same  formation  in  the  medulla  ;  and.  as  in  the  medulla,  it 
contains  two  fields — an  inner  and  an  outer.  The  former  is 
located  between  the  nerve-roots  of  the  sixth  pair  of  cranial 
nerves,  they  continuing-  anteriorly,  as  do  the  hypoglossal 
nerves.  From  the  scanty  supply  of  nerve-cells  and  conse- 
quent lack  of  color,  this  area  is  called  the  formatio  reticularis 
alba.  The  outer  field  is  located  between  the  nerve-roots  of 
the  sixth  and  seventh  pairs  of  cranial  nerves.  As  it  is  rich  in 
nerve-cells,  it  is  called  the  formatio  reticularis  grisea.  The  raphe 
exists  in  the  pons  as  in  the  medulla,  but  extends  anteriorly  only 
to  its  transverse  fibers.  In  the  formatio  reticularis  exist  cell 
groups,  continuations  of  like  groups  in  the  medulla,  for  the 
origin  of  the  facial,  abducens,  and  in  part  of  the  trigeminal 
nerves,  and  just  posterior  to  the  pyramids  are  the  tracts  of  fibers 
— the  corpora  trapezoidea — already  described. 

In  the  anterior  part  of  the  formatio  reticularis,  surrounded  by 
these  fibers,  exist  the  superior  olivary  bodies.  The  two  divi- 
sions of  the  fillet  or  lemniscus  occupy  a  large  part  of  the  antero- 
lateral field  of  the  formatio  reticularis,  the  lateral  fillet  beinof 
located  along  the  outer  periphery  and  meeting  the  mesial  fillet, 
which  is  located  dorsal  to  the  deep  transverse  fibers  of  the  pons, 
at  almost  a  right  angle.  Thus  the  fillet  is  seen  to  occupy  a  large 
part  of  the  anterolateral  region  of  the  tegmentum,  as  the  space 
occupied  by  the  formatio  reticularis  is  called.  The  fillet  is  di- 
vided into  two  distinct  bundles  of  fibers, — a  mesial  fillet  and  a 
lateral  fillet, — the  anatomic  and  physiologic  relations  of  which 
are  entirely  distinct.  The  mesial  fillet  represents  the  combined 
axones  from  the  cells  of  the  nuclei  cuneati  et  gracilis  and  from 
the  cells  of  the  sensory  end  nuclei  of  all  the  cranial  nerves  of 
the  opposite  side  except  the  auditory,  the  axones  having  decus- 
sated in  the  raphe.  Some  of  the  axones  and  collaterals  of  the 
mesial  fillet  that  have  come  from  the  nucleus  cuneatus  end  about 
the  cells  of  the  formatio  reticularis  of  the  pons  and  those  of  the 
anterior  and  posterior  corpus  quadrigeminum  ;  other  fibers  pass 
to  the  lenticular  nucleus  of  the  same  and  of  the  opposite  side,  while 
many  reach  the  parietal  lobe  of  the  brain  through  the  posterior 


THE    MEDULLA  OBLONGATA,  OR    BULB.  i8i 

division  of  the  internal  capsule.  The  fibers  fi-om  the  nucleus 
gracilis  and  end  nuclei  of  the  sensory  cranial  nerves  end  in  the 
ventral  part  of  the  optic  thalamus  (Monakow).  From  the  cells 
of  the  optic  thalmus  axones  pass  through  the  posterior  limb  of 
the  internal  capsule  and  radiate  toward  the  parietal  lobe. 

The  lateral  fillet  or  lemniscus   is  the  central  auditory  tract, 


Fig.  90. — Transverse  Section  through  the  Pons,  in  the  Region  of  the  Crossing 
OF  THE  Fourth  Nerve  jn  the  Dorsal  Medullary  Velum. — {Afte7-  Koelliker.) 

Br.C.  Superior  cerebellar  peduncles.  Vd.  Descending  cerebral  root  of  fifth  nerve.  IVd. 
Fourth  nerve  of  right  side.  Fl.  Posterior  longitudinal  bundle.  Tg.  Tegmentum  or  sub- 
stantia reticularis.  LM.  Median  lemniscus  or  fillet.  LI.  Lateral  lemniscus  or  fillet.  P. 
Pyramidal  fibers  between  the  superficial  and  deep  transverse  pons  fibers. 

being  composed  of  axones  from  the  end  nuclei  of  the  auditory 
nerve  and  the  superior  oHvary  body  ;  it  then  passes  to  the  pos- 
terior corpus  quadrigeminum,  and  thence,  by  means  of  its 
brachium  posterioris,  through  the  extreme  posterior  part  of  the 
posterior  hmb  of  the  internal  capsule,  and  radiates,  via  the  corona 
radiata,  to  the  first  and  second  temporosphenoid  gyri. 


i82  CENTRAL   NERVOUS  SYSTEM. 

On  each  side  of  the  median  line  in  tlie  posterior  part  of  the 
reticular  formation  is  the  triangular  area  of  longitudinal  fibers — 
the  posterior  longitudinal  bundles.  Beneath  the  ependyma  of 
the  fourth  ventricle,  and  lateral  to  these  bundles,  exist  a  number 
of  highly  pigmented  nerve-cells,  called  the  substantia  ferruginea. 
Just  external  to  the  posterior  longitudinal  bundle  of  fibers,  in  the 
loop  formed  by  the  bends  qf  the  facial  nerve,  is  a  collection  of 
large  multipolar  nerve-cells,  which  give  origin  to  the  abducens 
or  sixth  pair  of  cranial  nerves. 

Slightly  dorsolateral  to  the  nucleus  of  the  abducens  is  the 
dorsal  or  chief  auditory  nucleus,  which  occupies  a  large  field. 
External  and  a  little  dorsal  to  this  nucleus  is  the  nucleus  of 
Deiter  and  Bechterew,  which  has  already  been  described.  In 
front,  and  at  the  side  of  Deiter's  nucleus,  is  the  large  bundle 
of  fibers  of  the  restiform  body,  or  the  inferior  cerebellar 
peduncle. 


THE  NUCLEI  OF  ORIGIN  OF  THE  TRIGEMINAL  NERVE. 

This  nerve  has  two  roots  on  each  side — an  anterior  or  motor, 
the  smaller,  and  a  posterior,  the  sensory.  Both  roots  appear  at 
the  side  of  the  pons,  just  above  its  middle.  The  motor  root 
consists  of  the  axones  from  the  cells  of  the  motor  nucleus  of  this 
nerve  in  the  pons.  The  sensory  root  is  made  up  of  the  axones 
of  the  monopolar  cells  of  the  Gasserian  ganglion,  which  is 
located  in  a  fossa  near  the  apex  of  the  petrous  portion  of  the 
temporal  bone.  The  axones  of  these  monopolar  cells  each 
divide  into  two  divisions,  one  of  which  passes  peripherally,  form- 
ing the  great  sensory  nerve  of  the  face,  while  the  other  passes 
centrally,  entering  the  pons,  where  it  bifurcates,  one  division 
passing  slightly  upward,  the  other  downward,  both  giving  off 
very  fine  collaterals.  The  former,  those  which  pass  upward, 
enter  the  enlarged  termination  of  the  substantia  gelatinosa  of  the 
posterior  horn,  ending  about  the  small  nerve-cells  therein  con- 
tained, and  thus  this  termination  may  be  considered  as  the  end 
nucleus  of  this  set  of  fibers.  The  latter,  the  descendino-  branches 
(spinal  portion  of  this  nerve),  pass  downward  as  far  as  the 
beginning  of  the  motor  crossway  or  the  upper  level  of  the  first 
cervical  segment.     They  form  crescentic  bundles,  one  for  each 


THE  MEDULLA  OBLONGATA,  OR  BULB. 


183 


side,  which  are  located  just  external  and  slightly  lateral  to  the 
substantia  gelatinosa  of  the  posterior  horns,  occupying  about 
the  same  relative  position  to  the  heads  of  the  posterior  horns  as 
do  the  tracts  of  Lissauer  in  the  spinal  cord.  These  bundles  of 
fibers  gradually  diminish  in  size  from  above  downward.  In 
their  course  they  give  off,  nearly  at  right  angles,  a  large  number 
of  fine  collaterals.     The  main  branches,  with  many  of  their  col- 


FiG.  91.— Lateral  Sagittal  Section  through  the  Pons  and  Cerebellum  of  a 
Fetal  Mouse. — [Afier  Ratnott  y  Cajal.) 

A.  Sensory  root  of  the  fifth  nerve  divided  into  (a)  ascending  and  descending  (b)  branches.  C. 
Terminal  ramifications  of  the  ascending  branch,  d.  Root-fibers  passing  downvv^ard.  e. 
Posterior  part  of  the  descending  sensory  root.  B.  Bifurcation  of  the  vestibular  nerve, 
whose  ascending  branch  (g)  goes  to  the  cerebellum,  and  whose  descending  branch  (f)  goes 
to  the  medulla.  G.  Superior  cerebellar  peduncle.  D.  Descending  cerebellar  fibers.  E. 
Corpus  restiforme  (inferior  cerebellar  peduncle).  F.  Lateral  fillet  or  lemniscus.  H. 
Corpus  trapezoides.     O.   Corpus  dentatum. 


laterals,  end  in  fine,  brush-like  expansions  about  the  multipolar 
nerve-cells  existing  in  the  substantia  gelatinosa  of  the  posterior 
horns,  which  latter  may  be  considered  as  continuous  end  nuclei 
for  these  descending  branches,  hence  explaining  the  reason  for 
the  statement  above,  that  these  bundles  gradually  diminish  in 
size  from  above  downward.    Other  collaterals  from  the  descend- 


1 84 


CENTRAL  NERVOUS  SYSl KM. 


mvr  branches,  probably  comprising-  all  the  remainder,  presumably 
reflex  in  function,  end  in  fine  arborizations  about  the  cells  ot  the 
motor  nuclei  of  the  hypoglossal,  facial,  and  trigeminal  nerves. 
The  axones  from  the  cells  of  the  sensory  end  nuclei  of  the  tri- 
geminal nerves  pass  in  curves  (internal  arcuate  fibers),  decussate 
in  the  raphe,  and  pass  as  longitudinal  fibers  into  the  mesial  fillet 
or  lemniscus  of  each  side,  thus  forming-  the  central  sensory 
tracts  of  these  nerves.  These  longitudinal  fibers  give  off  in 
their  course  collaterals,  which  end  about  the  large  multipolar 
nerve-cells  of  the  formatio  reticularis. 


Fig.   92. — MiCROPHOToGRAPH 


,    -,..    ,  ....     IIIROUGH    THE  MeDII.I.A  OK  A   MlMAN    FeTLS 

OF  Seven  Months. 
Showing  axones  and  collaterals  of  the  trigeminal  nerve  entering  the  enlarged  caput  posterioris. 


The  motor  root,  also  called  the  nervus  masticatorius,  be- 
cause it  ennervates  the  muscles  of  mastication,  comes  chiefiy 
from  the  motor  nucleus  in  the  pons,  but  it  receives  an  accession 
of  fibers  from  a  nucleus  v^'hich  is  located  beneath  and  lateral 
to  the  aqueduct  of  Sylvius. 

The  chief  motor  nucleus  of  each  side  is  a  collection  of  multi- 
polar nerve-cells  located  slightly  backward  and  a  little  external 
to  the  sensory  end  nucleus  in  the  pons,  and  also  slightly  dorsal 


THE  MEDULLA  OBLONGATA,  OR  BULB.  1S5 

to  the  nucleus  of  the  facial,  of  which  it  is  probably  an  upward 
termination.  The  axones  of  these  cells  pass  ventrolaterally,  and 
issue  from  the  side  of  the  pons  as  a  small  bundle  of  fibers,  just 
ventral  to  the  sensory  root,  the  two  roots  being  separated  from 
each  other  by  a  small  bundle  of  transverse  pontine  fibers.  A 
few  axones  from  the  cells  of  the  median  part  of  this  nucleus 
pass  dorsally  in  curves  across  the  median  line  or  raphe,  and 
unite  with  the  motor  roots  of  the  opposite  side  ;  hence  each 
motor  root  receives  a  small  number  of  fibers  from  the  nucleus 
of  the  opposite  side. 

The  accessory  nucleus,  the  cells  of  which  give  origin  to  the 
descending  trigeminal  or  cerebral  root-fibers,  consists  of  a  col- 
lection  of  large,  somewhat  spheric  or  pear-shaped  cells,  which 
are  probably  multipolar  in  character,  although  it  is  usual  to 
describe  them  as  unipolar  nerve-cells.  No  dendrites  can  be 
discovered  coming  from  these  cells  after  they  have  been  stained 
with  silver  nitrate.  In  carmin-stained  specimens,  however,  den- 
drites can  usually  be  seen.  They  are  located  deep  beneath,  and 
lateral  to,  the  aqueduct  of  Sylvius,  extending  as  far  brainward 
as  the  corpus  quadrigeminum.  The  cells  of  this  nucleus  give 
off  single  thick  axis-cylinders,  which  course  downward  until  they 
reach  the  neighborhood  of  the  chief  motor  nucleus,  where  they 
branch,  one  branch  ending  in  a  plexus  of  fibers  about  a  motor 
cell  of  the  chief  nucleus  (Lugaro,  Ramon  y  Cajal),  the  other 
branch  joining  the  root-fibers  from  the  same  nucleus. 

The  Cerebral  Connections  of  the  Trigeminal  Nerve. — 
The  sensory  end  nucleus  of  the  trigeminal  nerve  is  connected 
with  the  opposite  sensorimotor  area  by  means  of  axones  which 
leave  this  nucleus  and  cross  in  the  raphe  to  pass  brainward 
in  the  mesial  fillet  of  the  opposite  side. 

The  motor  area  for  the  masticatory  muscles,  which  is  located 
probably  in  the  lower  part  of  the  ascending  frontal  gyrus,  is 
related  with  the  motor  nucleus  of  the  opposite  side  by  fibers 
which  leave  this  area  and  join  the  pyramidal  tract.  According 
to  some  observers,  fibers  from  the  sensory  trigeminal  roots  pass 
dorsolaterally,  enter  the  lateral  part  of  the  restiform  body, 
where  they  commingle  with  fibers  of  the  direct  sensory  cere- 
bellar tract,  and  pass  to  the  cerebellum.  This  cerebellar  con- 
nection of  the  trigeminal  nerve  is  denied  by  Bechterew. 


CHAPTKR  IV. 

THE  CEREBELLUM  OR  EPENCEPHALON. 

The  cerebellum,  or  little  brain,  is  located  in  the  inferior 
occipital  fossa.  Above  it  are  the  occipital  lobes,  separated  trom 
it  by  a  strong  process  of  dura  mater — the  tentorium  cerebelli. 
In  form  the  cerebellum  is  irregularly  oval  or  oblong,  its  greatest 
diameter,  7.5  to  10  cm.  (three  to  four  inches),  being  from  side 
to  side.  It  measures  5  to  53^  cm.  (2  to  2]/^  inches)  antero- 
posteriorly.  Its  greatest  thickness  is  at  its  ventral  portion, 
where  it  is  about  five  cm.,  or  two  inches.  Toward  the  periphery 
of  the  hemispheres  it  becomes  quite  thin,  being  at  the  periphery 
only  about  one  cm.,  or  five  lines,  in  thickness.  Its  average 
weight  in  the  adult  is  about  170  gm.,  or  5^  ounces.  In  the 
infant  it  is  much  smaller  in  proportion  to  the  entire  encephalon 
than  in  the  adult.  It  is  composed  of  two  hemispheres,  joined 
by  a  middle  portion  or  lobe,  which,  from  its  shape  and  from  the 
appearance  given  to  it  by  numerous  transverse  ridges  upon  it, 
is  called  the  worm,  vermis,  or  vermiform  process.  This  division 
into  hemispheres  is  much  more  apparent  on  the  under  surface, 
owing  to  a  broad,  shallow  depression  or  sulcus, — the  vallecula,  or 
little  valley, — which,  running  anteroposteriorly,  separates  them. 
The  vallecula  lodges  the  posterior  part  of  the  medulla  oblon- 
gata, and  from  it  projects  the  inferior  part  of  the  middle  lobe  or 
worm,  called  the  inferior  vermiform  process.  The  latter  forms, 
in  a  general  way,  the  roof  of  the  fourth  ventricle,  and  lies  behind 
and  below  the  corpora  quadrigemina.  The  cerebellum  has  on 
its  anterior  and  posterior  surfaces  deep  depressions, — the  ante- 
rior and  posterior  incised  notches, — which  are  continuous  with 
the  vallecula.  In  the  anterior  notch,  which  is  broader,  rests  the 
posterior  corpora  quadrigemina,  while  the  posterior  notch,  which 
is  shallower,  contains  the  falx  cerebelli.     The  bottom  of  these 


THE  CEREBELLUM  OR  EPENCEPHALON. 


187 


notches  Is  formed  by  the  worm,  while  the  sides  are  composed  of 
the  cerebellar  hemispheres.  The  cerebellum  is  divided  into  an 
upper  and  a  lower  surface  by  a  great  horizontal  fissure,  which 
begins  at  its  anterior  margin  and  extends  circumferentially  to 
the  median  line  behind. 

The  upper  surface  is  convex  at  its  middle  portion  and  grad- 
ually slopes  toward  its  periphery.  It  consists  of  two  hemi- 
spheres connected  by  a  convex  median  lobe,  the  superior  vermis 


Fig.  93. — Figure  Showing  the  Three  Pairs  of  Cerebellar  Pedunxles. — {After 
Hirschfeld  and  Leveille,  from  Sappey.) 

On  the  left  side  the  three  cerebellar  peduncles  have  been  cut  short ;  on  the  right  side  the  hemi- 
sphere has  been  cut  obliquely  to  show  its  connection  with  the  superior  and  inferior 
peduncles.  I.  Median  groove  of  the  fourth  ventricle.  2.  The  same  groove  at  the  place 
where  the  auditory  striae  emerge  from  it  to  cross  the  floor  of  the  ventricle.  3.  Inferior  or 
restiform  body.     4.  Funiculus  gracilis.     5,5.   Superior  peduncle. 

On  the  right  side  the  dissection  shows  the  superior  and  inferior  peduncles  crossing  each  other  as 
they  pass  into  the  white  center  of  the  cerebellum.  7,  7.  Lateral  grooves  of  the  crura  cerebri. 
8.    Corpora  quadrigemina. 


or  worm.  The  latter  is  of  great  physiologic  importance,  since 
its  experimental  removal  in  lower  animals  and  pathologic 
changes  in  it  in  man,  such  as  a  tumor,  hemorrhage,  injuries,  etc., 
produce  disturbances  of  coordinated  movements  and  difficulty 
in  the  maintenance  of  equilibrium.  This  proves  that  this  central 
portion  or  worm  is  principally  concerned  in  the  adjustment  of 
coordinated  movements  and  the  maintenance  of  equilibrium. 
The  cerebellum  is  connected  with  the  remainder  of  the  cerebro- 


i88  CENTRAL  NERVOUS  SYSTEM. 

spinal  axis  l)y  three  large  bundles  of  nerve-fibers — the  superior. 
middle,  and  inferior  cerebellar  peduncles.  The  superior  pedun- 
cles (processus  ad  cerebrum)  appear  to  come  from  the  region 
just  'beneath  the  corpora  quadrigemina,  where  they  decussate, 
extending  from  one  cerebral  hemisphere  to  the  opposite  cere- 
bellar hemisphere.  In  their  course  they  run  outward  and  back- 
ward, and  before  entering  the  cerebellum  they  diverge,  forming 
the  lateral  boundaries  of  the  upper  half  of  the  fourth  ventricle, 
and  are  united  by  the  valve  of  Vieussens,  or  the  superior  medul- 
lary velum.  They  then  appear  to  pass  into  the  nucleus  den- 
tatum  of  the  cerebellum  of  each  side.  The  superior  cerebellar 
peduncles  connect  the  cerebellum  with  the  cerebrum.''' 

The  middle  peduncles  (processus  ad  pontem)  consist  of  the 
before-mentioned  superficial  and  deep  sets  of  transverse  fibers, 
some  of  which  pass  from  the  pons  to  the  cerebellar  cortex  and 
some  from  the  cerebellar  cortex  to  the  pons,  forming  the  great 
transverse  commissure  of  the  cerebellum.  These  are  located 
external  and  anterior  to  the  superior  peduncles. 

The  inferior  peduncles  (corpora  restiformia ;  processus  ad 
medullam)  serve  to  connect  the  medulla  and  the  spinal  cord  to 
the  cerebellum  by  means  of  long-  tracts  of  fibers.  As  they  pass 
upward  and  backward  on  their  way  to  the  cerebellum  they 
diverge,  and  assist  in  formino-  the  lateral  boundaries  of  the  lower 
part  of  the  fourth  ventricle.  They  end  chiefly  in  the  cortex  of 
the  superior  worm  of  the  cerebellum. 


THE  VERMIS,  OR  WORM. 

SUPERIOR  SURFACE. 

This  surface  presents  a  transversely  ridged  appearance,  and 
has,  from  before  backward,  the  following  lobules  :  First,  the  lin- 
gula  is  most  anterior,  between  the  superior  peduncles  of  the  cere- 
bellum, resting  upon  the  superior  medullary  velum.  It  consists 
of  a  tongue-shaped  process  composed  of  four  or  five  transverse 
lamina;,  which  latter  are  prolonged  over  the  superior  peduncles, 

*  While  the  course  of  the  superior  cerebellar  peduncles  appears  to  extend  as  above  described, 
yet  most  of  the  fibers  have  been  proved  to  have  an  opposite  course — i.  e.,  from  the  corpus  den- 
tatum  toward  the  cerebrum. 


THE   CEREBELLUM   OR    EPENCEPHALON.  189 

and  are  called  the  frsenulum  lingulae.  Its  basal  part  is  con- 
tinuous with  the  lobus  centralis.  Next  is  the  lobus  centralis, 
which  is  just  back  of  the  lingula,  being-  separated  from  it  by  an 
interlobular  fissure,  the  precentral ;  it  is  in  front  of  the  culmen, 
which  overlaps  it.  This  lobule,  with  the  lingula,  forms  the 
bottom  of  the  anterior  incised  notch.  The  next  lobule  is  the 
monticulus  cerebelli,  which  forms  the  greater  part  of  the  con- 
vexity of  the  worm,  its  anterior  portion  being  called  the  culmen, 
or  height,  the  posterior  part,  the  declive.  The  monticulus  is 
separated  from  the  central  lobe  by  the  postcentral  fissure.  The 
culmen  must  be  lifted  in  order  to  expose  the  central  lobe,  and 
the  declive,  when  raised,  exposes  a  lobule  just  posterior  to  it, 
the  folium  cacuminis,  which  is  a  small  lobule  next  in  size  to  the 
lingula,  and  continuous  laterally  with  the  posterior  superior  or 
semilunar  lobes. 


THE  INFERIOR  SURFACE. 

This  surface,  from  before  backward,  presents  the  foUowino- 
lobules  :  First,  the  nodulus,  which  bears  the  same  relation  to  the 
inferior  vermiform  process  as  does  the  lingula  to  the  superior. 
It  occupies  the  anterior  extremity  of  the  vermis,  and  is  com- 
posed of  a  few  transverse  laminae  separated  by  slight  fissures. 
It  is  the  smallest  lobule  of  the  inferior  worm.  The  lateral  part 
of  the  inferior  medullary  velum  is  continued  on  each  side  of 
the  nodule  as  a  thin  white  band  which  serves  to  connect  the 
nodulus  with  the  flocculus. 

Second,. the  uvula,  located  just  dorsal  to  the  nodulus,  forms 
the  greater  part  of  this  surface  of  the  worm.  It  increases  in 
size  from  before  backward,  and  attains  its  greatest  size  close  to 
the  pyramid  ;  it  is  separated  from  the  hemispheres  by  a  deep 
fissure, — the  sulcus  valleculae, — and  is  connected  with  the  amyg- 
dalae, or  tonsils,  which  exist  on  each  side,  by  a  corrugated 
grayish  ridge,  the  furrowed  band,  which  crosses  the  sulcus  valle- 
culae. Its  surface  is  marked  by  three  or  four  transverse  intra- 
lobular fissures. 

Third,  the  pyramid.  The  posterior  portion  of  the  inferior 
worm  is  called  the  pyramid.      It  is    a  large,    conic  projection 


I90 


CENTRAL  NERVOUS  SYSTEM. 


consisting  of  three  or  four  transverse  laminae,  separated  by  fis- 
sures ;  the  sulcus  valleculct  separating  it  from  the  hemispheres. 
It  is  connected  with  the  digastric  lobule  by  a  narrow  ridge  of 
ti-ray  matter  at  the  bottom  of  the  sulcus  valleculse  ;  from  the 
inferior  surface  of  the  pyramid,  extending  anteriorly  over  the 
superior  surface,  is  a  process  called  the  tuber  valvulae.  The 
ricrht  and  left  sulci  valleculae  are  the  deep  anteroposterior 
o-rooves  on  the  inferior  surface  of  the  cerebellum  which  sepa- 
rate the  inferior  worm  from  the  cerebellar  hemispheres. 


LOBULES  OF  THE  SUPERIOR  OR  DORSAL  SURFACE 
OF  THE  CEREBELLAR  HEMISPHERE. 

First,  the  lobulus  quadratus,  or  square  lobe,  is  located  on 
each  side  of  the  monticulus. 

Second,  the  posterior  superior  semilunar  lobe  occupies  the 
posterolateral  part  of  the  dorsal  surface.  It  is  connected  with 
its  fellow  of  the  opposite  side  by  the  folium  cacuminis. 


LOBULES  OF  THE  INFERIOR  SURFACE  OF  THE 
CEREBELLAR  HEMISPHERE. 

First,  the  flocculus,  situated  on  each  side  of  the  nodulus  below 
the  middle  peduncles  and  posterior  to  the  sensory  nuclei  of  the 
pneumogastric  nerves. 

Second,  the  amygdalum,  or  tonsil,  is  located  on  each  side  of 
the  uvula.  It  is  connected  with  the  uvula  and  projects  into 
the  fourth  ventricle. 

Third,  the  cuneate  or  diagastric  lobule  is  a  large,  somewhat 
wedge-shaped  or  triangular  area,  located  just  external  to  the 
amygdalum  and  pyramid,  being  attached  to  the  latter  by  a  grayish 
rido-e  crossing  the  bottom  of  the  sulcus  valleculse.  Its  laminae 
are  curved,  with  their  concavity  forward  and  inward.  It  is  sepa- 
rated from  the  tonsil  on  each  side  by  a  fissure  in  front  of  the 
pyramid,  called  the  prepyramidal  fissure.  The  tonsil  when  re- 
moved leaves  a  hollow  depression  on  the  mesial  surface  of  this 
lobule,  which,  because  of  its  resemblance  to  a  bird's  nest,  is 
called  the  nidus  avis. 


'_M^M 

^  A.  f .  N .  ^^^^^m^fete^^ 

^^^^^HV 

LC                                         3^ 

^K^taf^^^^^' 

|SW^.^        .U||H| 

WHaHH| 

^^^^Hfe^.^^                                                                            ^^^^^^^^^^^^m 

^^K^^^H 

FrknS            -m^^ 

^^^^^^^^H 

''^J^:^SSt   : "'      -^^^^^^r^ 

^J-..^^H^ 

^■% 

Fig.  94. — Superior  Surface  of  the  Cerebellum. 
A.I.N.  Anterior  incised  notch.     L.C.   Central  lobe.     C.  Culmen.     M.   Monticulus.     D.  De- 
clive.      P.I.N.    Posterior  incised  notch.     L.I.S.    Inferior  semilunar  lobe.     H.F.    Great 
horizontal  fissure.      L.S.  S.    Superior  semilunar  lobe.     L.  Quad.   Quadrate  lobe. 


Fig.  95. — Inferior  Surface  of  the  Cerebellum. 
A.I.N.       Anterior   incised   notch.       F.    Flocculus.       L.Q.    Lobus    quadratus. 
U.    Uvula.      P,    Pyramid.     P.I.N.    Posterior   incised    notch.     T.    Tonsil 
cuneatis.     L.G.    Lobus  gracilis.     L.I.S.   Lobus  inferioris  semilunaris. 


N.    Nodulus. 
L.C.    Lobus 


191 


THE  CEREBELLUM  OR  EPENCEPHALON. 


»93 


Fourth,  the  lobus  gracilis,  or  slender  lobe,  is  just  external  to 
the  cuneate  lobe,  around  the  periphery  of  which  lobe  it  extends. 
It  is  also  connected  with  the  pyramid.  It  has  along  its  periphery 
the  inferior  semilunar  lobule. 


MINUTE  ANATOMY  OF  THE  CEREBELLUM. 

The  cerebellum  consists  of  gray  and  white  matter,  the  former 
surrounding  the  latter  and  forming  its  cortex.    The  gray  matter 


Fig.  96.— Microphotograph  of  Cerebellar  Cortex.     Showing  the  molecular  and  granu- 
lar layers  and  the  arrangement  of  the  arbor  vitse. 

consists  of  foliated  laminae,  each  one  of  which  has  a  central  core 
of  white  matter,  and  is  formed  of  secondary  and  tertiary  folia, 
which  arrangement  gives  to  sections  of  the  cerebellum  the  char- 
acteristic arbor  vitse  appearance.  The  gray  matter  dips  into  the 
various  fissures  and  sulci,  and  is  thus  spread  over  a  large  extent 
of  surface,  which  surface  is  nearly  as  great  as  that  covered  by 
the  cortex  of  the  cerebrum.    The  white  matter  is  more  abundant 


194  CENTRAL  NERVOUS  SYSTEM. 

in  the  hemispheres  than  in  the  vermis.  In  the  former  it  is  irreg"- 
iilar  in  contour  and  is  somewhat  oblong-.  In  tlie  latter  it  is 
scant  and  arranged  in  a  quadrangular  shape  ;  hence  the  name 
corpus  trapezoideus.  From  the  central  white  stem  of  the  vermis 
a  thin  extension  of  white  matter  passes  out  which  bridges  across 
the  superior  peduncles  and  forms  the  roof  of  the  upper  part  of 
the  fourth  ventricle,  upon  which  the  lingula  rests.  This  ex- 
tension is  the  before-mentioned  superior  medullary  velum,  or 
valve  of  \  ieussens.  Below,  a  similar  process  of  white  matter 
extends  from  the  cerebellum  and  forms,  with  a  process  of  pia 
mater,  the  tela  choroidea  inferior,  the  roof  of  the  lower  part  of 
the  fourth  ventricle,  and  is  called  the  inferior  medullary  velum. 
The  white  matter  consists  of  medullated  nerve-fibers,  which  form 
short  and  long  tracts,  which  will  be  described  later.  Deep 
in  the  central  part  of  the  w^hite  matter  of  each  hemisphere  and 
reaching  below,  nearly  to  the  fourth  ventricle,  is  embedded  a 
nucleus — the  corpus  dentatum,  or  ciliare.  Each  dentate  body 
consists  of  a  convoluted,  sinuous  bag  of  gray  matter,  having  a 
dorsal  and  a  ventral  lamina,  with  an  opening  or  hilum  on  its 
ventral  and  mesial  surface.  It  contains  a  rich  plexus  of  nerve- 
fibers  with  a  large  number  of  multipolar  nerve-cells  in  their 
meshes.*  These  cells  vary  from  30  to  40  ft  in  diameter,  and 
possess  numerous  dendritic  processes  which  come  off  chiefly 
from  the  inner  portion  of  the  cell-body.  The  neuraxones  from 
these  cells,  after  giving  off  w^ithin  the  corpus  dentatum  one  or 
two  collaterals,  pass  out  of  the  hilum  into  the  superior  cerebellar 
peduncles,  of  which  they  form  the  great  bulk.  The  dentate 
bodies  resemble  very  closely  the  inferior  olivary  bodies.  This 
resemblance  is  heightened  by  the  fact  that  three  smaller  nuclei 
lie  close  to  each — namely,  the  roof  nucleus  oi  Stilling,  or  tegjnental 
nucleus,  the  nucleus  embolliformis,  and  the  nucleus  globosus.  The 
roof  or  tegmental  nucleus  belongs  properly  to  the  worm.  It  is 
about  10  mm.  long,  and  is  an  oblong  mass  of  gray  matter 
on  each  side  of  the  middle  line,  just  above  the  ependyma 
of  the  fourth   ventricle,    from   w^iich   it  -is  separated   by  a  thin 


*  It  is  probable  that  many  of  the  fibers  which  form  the  network  within  the  corpora  dentata 
are  the  terminations  of  tlie  axones  comina:  from  the  cells  of  the  nuclei  rubri. 


. 

c*^ 

^gm 

• 

£ 

^J0^g^ 

^C^^ 
^>^''" 

WM       ^^^^B 

^ 

1^ 

*ft 

Hr 

Fig.  97. — Section  Through  Cerebellum  to  Show  the  Dentate  Nuclei  and  White 

Matter  of  the  Hemispheres. 
CO.   Dentate  nucleus.     N.   Nodule.     T.    Tonsil.     W. M.  White  matter  ot   cerebellar  hemi- 
sphere. 


y 


Fig.  98. — Microphotograph  of  a  Section  through  the  Corpus  Dentatum  of  the 
Human  Cerebellum.  Containing  three  large  (multipolar)  polygonal  cells.  Method  of 
Berkley. 

195 


THE   CEREBELLUM   OR    EPENCEPHALON. 


197 


layer  of  white  matter.  The  nucleus  embolliformis  is  a  small, 
clavate  mass  of  gray  matter  located  mesial  to  the  hilum  of 
the  dentate  body.  Beneath  and  on  the  inner  side  of  this  nucleus 
is  the  nucleus  globosus.  The  fibers  which  surround  the  dentate, 
bodies  are  called  extracapsular  or  extraciliary  fibers.  From 
the  intricate  network  of  these  fibers,  resembling  the  hairs  of 
wool,  the  term  fleece  is  applied  to  this  portion.  These  fibers 
doubtless  come  from  the  cerebellar  cortex,  being  the  axis-cylin- 


."Ma 


Fig.  99. — MiCROPHOTOGRAPH    Showing  Basket   Cells   and   Fibers  Surrounding  the 
Bodies  of  two  Purkinje  Cells  (Human  Cerebellum).     Cox-Golgi  method. 


ders  of  the  cells  of  Purkinje.  Some  of  them  pierce  the  dentate 
body  of  each  side  and  issue  at  the  hilum,  assisting  in  the  forma- 
tion of  the  superior  peduncles,  while  most  of  them  surround 
the  dentate  bodies  and  are  probably  those  descending  fibers 
which  go  to  form  the  so-called  cerebello-olivary  tracts,  and  tracts 
of  Marchi  and  Lowenthal,  of  the  corpora  restiformia.  Others 
doubtless  pass  as  pontine  fibers,  assisting  in  the  formation  of  the 
middle  peduncles. 


198 


CENTRAL  NERVOUS  SYSTEM. 


THE  CORTEX  OF  THE    CEREBELLUM. 

The  cerebellar  cortex  is  divided  into  two  distinct  layers, 
between  which  are  the  characteristic  cells  of  the  cerebellum,  the 
cells  of  Purkinje.  The  first  or  outer  layer  is  termed  the  molecu- 
lar layer,  and  the  other  the  internal  granular  or,  from  its 
appearance,  the  rust-colored  layer.  The  molecular  layer  con- 
tains two  chief  forms  of  cells — outer,  small,  stellate  cells,  and 
inner,  basket  cells,  or  "  Korbzellen  "  of  the  Germans.  The  stel- 
late cells  are  small,  multipolar  cells,  10  or  15  u  in  diameter,  each 


-^^^i^ 


Fig.  100. — Granular  Cells  of  the  Inner  Layer,  with  Ascending  Neuraxones 
Branching  T-shaped  to  Form  the  Horizontal  Fibers  of  the  Molecular  Layer. 
— {After  Van  Gehuchten.) 

possessing  several  short  dendrites  which  repeatedly  ramify, 
many  of  them  assuming  a  horizontal  course.  Their  axis-cylinders, 
or  neuraxones,  are  delicate  processes  of  considerable  length, 
and  possess  several  collateral  branches.  The  axones  pass  ver- 
tically, entering  the  upper  part  of  the  molecular  layer,  forming 
there  an  intricate  maze  of  fibers.  Their  final  destination  has  not 
been  traced.  The  basket  cells,  which  are  the  innermost  of  the 
molecular  layer,  are  slightly  larger  than  the  stellate  cells,  being 
from  II  to  20  a  in  diameter,  and  multipolar  in  form.  Each  cell 
possesses  several  dendrites  which  ramify  in  the  innermost  part  of 


THE  CEREBELLUM  OR  EPENCEPHALON. 


199 


the  molecular  layer,  and  a  long,  thick  neuraxone.  It  is  of 
interest  to  note  that  these  axones  start  from  the  cell-bodies  as 
very  fine,  horizontal  processes  which  increase  in  size  until  they 
become  two,  three,  or  even  four  times  their  original  thickness. 
Each  neuraxone  passes  out  horizontally  from  the  cell-body  and 
gives  off,  at  varying  distances,  numerous  branching  collaterals, 
which  pass  vertically  downward  until  they  reach  close  to   the 


Fig.  ioi. — Microphotograph  Showing  the  Moss-like  Fibers   of  the  Cerebellum. 

Cox-Golgi  method. 

bodies  of  the  Purkinje  cells,  where  the  fibers  end  in  tuft-like 
expansions,  forming  a  basket-like  network  about  each  Purkinje 
cell ;  hence  their  name,  "basket  cells"  (Fig.  99). 

The  inner  or  rust-colored  layer  is  made  up  of  a  large  number 
of  closely  arranged,  granular,  multipolar  cells,  each  possessing 
a  large  nucleus  and  nucleolus.  They  are  from  5  to  10  ff  in 
diameter,  and  give  off  a  large  number  of  branching,  dendritic 
processes  and  fine  neuraxones,  which  often  start  from  one  of 
the  short,  dendritic  processes.     These  neuraxones,  according  to 


200  CENTRAL  NERVOUS  SYSTEM. 

Ramon  y  Cajal,  pass  into  the  molecular  layer,  where  they  divide 
in  a  T-shaped  manner,  there  forming  horizontal  fibers.  It  is 
thought  by  Cajal  that  these  branches  end  about  the  dendritic  pro- 
cesses of  the  cells  of  Purkinje.  In  addition  to  the  before-men- 
tioned cells,  there  exist  large,  multipolar  cells,  which  belong  to  the 
second  type  of  Golgi — that  is,  possessing  short,  stout,  dendritic 
branches  which  occupy  parts  of  the  lower  molecular  and  upper 
granular  layers.  The  axis-cylinders  of  these  cells  repeatedly 
ramify  in  the  granular  layer,  forming  fine  interlacements.  It  is 
not  known  whether  or  not  they  are  connected  with  fibers  of  the 
underlying  white  matter.  Cajal  describes  a  large  number  of 
centripetal  fibers  which,  on  entering  the  granular  and  molecular 
layers,  branch  and  show  in  their  course,  at  their  points  of  branch- 
ing and  at  their  terminations,  irregular,  moss-like  thickenings. 
This  appearance  occurs  mainly  in  the  fibers  of  the  granular  layer. 
He  believes  .that  they  conduct  impulses  to  the  granular  cells  of 
this  layer.  He  describes  other  centripetal  fibers  entering  the 
molecular  layer,  there  branching  tree-like,  among  the  dendritic 
ramifications  of  the  cells  of  Purkinje  (Fig,  102). 


THE  CELLS  OF  PURKINJE. 

These  cells  exist  between  the  two  previously-described  layers, 
and  are  the  characteristic  cells  of  the  cerebellum.  They  are  of 
great  physiologic  importance  because  of  their  supposed  function, 
which  is  to  originate  impulses  which  serve  to  coordinate  the 
muscles  of  the  body,  and  thus  maintain  equilibrium.  They  are 
oval,  roundish,  or  flask-shaped  bodies,  35  to  70  /.i  in  diameter,  pos- 
sessing a  nucleus  and  nucleolus.  From  their  cortical  surface  are 
given  off  at  first  horizontal  or  oblique,  stout,  protoplasmic  pro- 
cesses, one  or  two  in  number,  which  soon  send  out,  nearly  at  right 
angles,  many  radiating  processes,  each  branching  like  a  tree, 
and  further  subdividing  into  many  smaller  branches.  These 
dendrites  are  covered  with  minute,  club-like  protuberances — the 
gemmules,  or  buds.  From  its  resemblance  to  a  tree,  this  rami- 
fication bears  the  name  arborization.  These  dendrites  almost 
entirely  occupy  the  molecular  layer,  each  dendrite  ending  in 
a    free    extremity,    which    often    curves    upon    itself    near    the 


THE   CEREBELLUM   OR    EPENCEPHALON.  201 

margin  of  the  cortex.  The  Purkinje  cells  possess  very  long, 
delicate  axis-cylinders,  which  pass  through  the  granular  layer, 
enter  the  white  matter,  and  form  the  chief  cortical  system  of 
fibers.  In  their  course  they  give  off  numerous  collaterals, 
which  pass  upward  through  the  granular  layer,  enter  the  mole- 
cular layer,  and,  according  to  Cajal,  come  into  contact  with 
the  dendritic  processes  of  these  cells.  He  believes,  by  this 
connection  of  collaterals  and  dendrites,  the  simultaneous  action 


Fig.  102. — MiCROPHOTOGRAPH  OF  Purkinje  Cell. 


of  many  of  these  cells  of  Purkinje  is  secured.  It  is  interesting 
to  note  that  the  axis-cylinders  of  these  cells  are  developed  much 
earlier  than  the  dendritic  processes. 

The  fibers  of  the  cerebellum  comprise  the  short  and  the  long. 
The  former,  or  association  fibers,  are  delicate  bundles  of  fibers 
lying  just  beneath  the  cortex,  serving  to  unite  adjacent  areas  of 
the  same  hemisphere.  The  long  or  projection  fibers  consist  of 
two   sets — centrifugal   and  centripetal.     The  former  represent 


202  CENTRAL  NERVOUS  SYSTEM. 

the  axones  from  the  cells  of  Purkinje  and  the  cells  of  the 
nuclei  dentata.  The  centripetal  fibers  are  those  which  proceed 
to  the  cerebellum  from  the  various  parts  of  the  cerebrospinal 
axis.  The  projection  fibers  as  a  whole  are  the  before-mentioned 
peduncular  system  of  fibers,  which  serve  to  bring  the  cerebellum 
into  relation  with  all  the  other  parts  of  the  central  nervous  sys- 
tem. There  are  three  cerebellar  peduncles — superior,  middle, 
and  inferior. 


THE  CEREBELLAR  PEDUNCLES. 

The  superior  peduncles,  also  called  the  brachia  conjunctiva, 
consist  of  bundles  of  nerve-fibers  which  have  their  chief  oriein 
in  the  cells  of  the  dentate  bodies,  and  are  the  before-mentioned 
intraciliary  fibers.  They  receive  in  addition  fibers  from  the  cells 
of  Purkinje.  They  then  pass  from  the  cerebellum  brainward  to 
the  region  of  the  posterior  corpora  quadrigemina,  beneath  which 
is  located  on  each  side  the  nucleus  ruber,  or  red  nucleus,  of  the 
tegmentum.  Below  and  close  to  each  nucleus  the  majority  of 
the  fibers  of  each  peduncle  decussate  with  their  fellows  of  the 
opposite  side  and  pass  to  the  opposite  nucleus,  ending  about  its 
nerve-cells.  A  few  fibers,  however,  do  not  decussate,  but  pass 
to  the  nucleus  ruber  of  the  same  side.  Thus  each  corpus 
dentatum  is  connected  with  both  nuclei  rubri,  but  chiefly  with 
the  nucleus  of  the  opposite  side.  Gudden,  Forel,  and  Marchi 
have  shown,  by  the  study  of  secondary  degeneration,  that  the 
fibers  of  these  peduncles  pass  chiefly  to  the  cells  in  the  posterior 
part  of  the  nuclei  rubri.  Many  of  them,  however,  pass  antero- 
laterally,  and  end  in  the  ventral  part  of  the  optic  thalami.  From 
the  cells  of  each  thalamus  new  neuraxones  pass  out  through  the 
posterior  part  of  the  internal  capsule,  and  radiate  toward  the 
cerebral  cortex,  to  terminate  probably  in  the  cortex  of  the 
parietal  and  central  convolutions,  thus  establishing  a  connection 
between  the  cerebellar  hemisphere  of  one  side  and  the  opposite 
cerebral  hemisphere.  The  superior  peduncles  contain,  in  addi- 
tion to  these  ascending  fibers,  some  which  degenerate  downward, 
and  these  latter  are  probably  the  axones  from  the  cells  of  the 
nuclei  rubri.  They  pass  to  the  corpora  dentata,  and  end  about 
the  cells  therein  contained. 


THE   CEREBELLUM   OR    EPENCEPHALON.  263 

THE  MIDDLE  PEDUNCLES. 

The  fibers  which  form  the  middle  peduncles  consist  in  part  of  the 
axones  from  the  cells  of  Purkinje,  which  pass  from  the  cerebellar 
cortex  in  a  transverse  manner,  ending  about  the  cells  of  the 
nuclei  pontis,  some  of  the  same,  others  of  the  opposite  side. 
Other  fibers  from  the  same  source  end  in  a  similar  manner 
about  the  cells  of  the  formatio  reticularis  of  both  sides,  thus, 
according  to  Bechterew,  establishing  a  connection  between  the 
cerebellum  and  the  remains  of  the  anterolateral  ground-bundles 
of  fibers,  which  also  pass  into  the  formatio  reticularis.  The  re- 
maining fibers  of  the  middle  peduncles  come  chiefly  from  the 
cells  of  the  nuclei  pontis,  being  their  axis-cylinders,  and,  after 
decussating  in  the  raphe,  pass  to  the  cortex  of  the  opposite 
cerebellar  hemisphere. 

These  peduncles  establish  a  connection  chiefly  between  the 
frontal,  temporal,  and  occipital  lobes  of  each  side  and  the  opposite 
cerebellar  hemisphere,  owing  to  the  fact  that  fibers  from  these 
lobes  end  about  the  cells  of  the  nucleus  pontis  of  the  same  side, 
and  the  axones  of  these  latter  cells  pass  to  the  opposite  cerebellar 
hemisphere,  forming  continuous  paths  of  conduction — the  so- 
called  frontocerebellar  and  temporo-occipital  cerebellar  tracts. 


THE  INFERIOR  CEREBELLAR    PEDUNCLES,  OR  CORPORA 

RESTIFORMIA. 

These  contain  fasciculi  of  fibers  which  come  from  several 
sources.  Those  which  have  been  most  thoroughly  studied  are 
the  following  : 

First,  the  direct  cerebellar  tracts,  or  columns  of  Flechsig, 
whose  fibers  are  the  neuraxones  from  the  cells  of  Clarke  and 
Stilling,  and  have  their  greatest  development  in  the  upper  lumbar 
and  lower  dorsal  segments ;  they  proceed  upward  along  the 
posterolateral  periphery  of  the  cord,  and  on  reaching  the 
medulla,  gradually  trend  backward  into  the  corpora  restiformia  ; 
they  then  pass  medianward  to  the  corpora  dentata,  and  termi- 
nate, according  to  Bechterew  and  von  Monakow,  without  de- 
cussation, in  the  cortex  of  the  superior  worm. 


204  CENTRAL   NERV(.)US   SYSTEM, 

Second,  two  small  bundles  of  fibers  pass  to  the  cerebellum 
from  the  nuclei  of  the  cokmins  of  Goll  and  Burdach.  The  first, 
or  the  posterior  external  arcuate  fibers,  pass  around  the  poste- 
rior periphery  of  the  cord,  and  reach  the  restiform  body  of  the 
same  side.  The  second  bundle,  which  comes  from  the  nuclei  of 
the  posterior  columns,  after  crossing  in  the  raphe  (interolivary 
fibers),  passes  around  the  periphery  of  the  anterior  pyramids  and 
olivary  bodies  and  joins  the  restiform  body  of  the  opposite  side. 
These  are  the  anterior  external  arcuate  fibers.  According-  to 
Bechterew,  these  fibers  pass  lateral  to  the  corpora  dentata  and 
end  in  the  cortex  of  the  superior  worm. 

Third,  fibers  pass  to  the  corpus  restiformc  from  the  lateral 
nucleus  of  the  medulla  of  the  same  side.  They  pass  to  the 
,  superior  worm. 

Fourth,  the  descendino-  cerebella:r  tracts  of  Marchi  and  Lowen- 
thai,  which  probably  have  their  origin  in  the  cerebellar  cortex, 
and  are  the  axones  from  the  cells  of  Purkinje.     They  degenerate 

Fig.  103. — Scheme  ok  the  Fihers  Passing  to  and  from  the  Cerebellum. 

The  fibers  of  the  superior  peduncles  are  indicated  by  Roman  numerals,  the  middle  peduncles  by 
letters,  and  the  inferior  peduncles  by  Arabic  numerals.  For  convenience,  both  ends  of  the 
fibers  are  marked. 

Inferior  Cerebellar  Pedtaule. — I.  Direct  cerebellar  tract.  2.  Anterolateral  descending  tract 
of  Lowenthal  and  Marchi.  3.  Fiber  from  posterior  nerve-root  decussating  in  anterior 
commissure  and  ending  about  a  cell  of  origin  of  Gowers'  tract.  4.  Postero-external  arcuate 
fibers  passing  from  the  nucleus  gracilis  and  cuneatus  of  the  same  side  via  the  restiform 
body  to  the  cerebellar  cortex.  5.  Internal  arcuate  fibers  from  the  nucleus  gracilis  and 
cuneatus  of  the  opposite  side,  decussating  in  the  raphe,  and  passing  around  the  opposite 
anterior  pyramid  to  join  the  restiform  body  opposite  to  their  origin.  6.  Cerebello-olivary 
tract  passing  from  the  cerebellar  cortex  to  the  opposite  olivary  body,  whence  the  tract  is 
continued  downward  by  axones  from  the  cells  of  the  olivary  body  in  the  lateral  column  to 
terminate  about  the  cells  of  the  spinal  cord  at  various  levels.  7.  The  vestibulocerebellar 
tract  passing  from  the  auditory  nucleus  to  the  cortex  of  the  superior  worm. 

Middle  Cerebellar  Peduncle. — A,  B.  Fibers  from  cells  of  Purkinje  passing  to  the  fomiatio  retic- 
ularis of  the  same  and  opposite  sides.  C.  Fiber  from  nucleus  pontis  passing  to  cerebellar 
cortex  of  opposite  side.  D,  E.  Fibers  from  cells  of  Purkinje  to  nucleus  pontis  of  same 
and  opposite  sides. 

Superior  Cerebellar  Peduncles. — I.  Fiber  from  corpus  dentalum  passing  to  optic  thalamus  of 
same  side.  II,  I\'.  Fibers  from  corpus  dentatum  passing  to  red  nucleus  of  the  same  and 
opposite  sides.  Ill,  V.  Fiber  from  red  nucleus  passing  to  corpus  dentatum.  VI.  Fiber 
from  red  nucleus  to  optic  thalamus.  \'\\.  Fiber  of  Gowers'  tract  passing  through  formatio 
reticularis,  arching  over  the  root  of  the  fifth  nerve,  and  reaching  the  superior  cerebellar 
peduncle,  passing  the  corpus  dentatum  of  the  same  side  and  sending  a  collateral  branch 
to  the  cerebellar  cortex. 

Th.  Optic  thalamus  ;  Crus,  crus  cerebri;  Pons,  pons  Varolii  ;  Med,  medulla  oblongata ;  S. 
C,  spinal  cord. 


Fig,  103. — Scheme  of  the  Fibers  Passing  to  and  from  the  Cerebellum. 


205 


THE  CEREBELLUM  OR  EPENCEPHALON.  207 

downward  and  have  been  traced  into  the  anterolateral  area  of 
the  cord,  they  probably  end  in  the  median  gray  matter. 

Fifth,  the  direct  sensory  cerebellar  tract — better  called  the 
acousticocerebellar  tract — joins  the  restiform  body  and  pro- 
ceeds, after  decussating,  to  the  opposite  roof  or  tegmental 
nucleus  and  nucleus  globosus.  This  tract  conveys  centripetal 
axones  from  Deiters'  nucleus,  thus  establishing  a  connection 
between  the  nucleus  vestibularis  of  the  auditory  nerve  and  the 
cerebellar  hemisphere  of  the  opposite  side.  This  tract  also 
contains  descending  fibers,  axones  of  the  cells  of  Purkinje,  which, 
according  to  Koelliker,  end  about  the  cells  of  the  nuclei  of  the 
posterior  columns,  and  probably  give  fibers  and  collaterals  to 
Deiters'  nucleus  and  the  nucleus  of  the  trigeminal,  pneumogas- 
tric,  and  glossopharyngeal  nerves.* 

Sixth,  the  large  tract  of  centrifugal  or  efferent  fibers,  known 
as  the  cerebello-olivary  tract,  whose  fibers  are  the  axones  of  the 
cells  of  Purkinje  of  the  same  side,  and,  after  having  decussated 
in  the  raphe,  end  about  the  cells  of  the  opposite  olivary  body.-|- 

In  addition  to  the  previously-mentioned  peduncular  system  of 
fibers,  the  cerebellar  hemispheres  are  connected  by  means  of 
two  commissures  which  exist  in  the  worm — an  anterior  and  a 
posterior.  The  anterior  commissure  of  Stilling  is  ventral  to  the 
roof  nucleus,  being  separated  from  the  latter  by  a  narrow  band 
of  fibers.  A  fasciculus  from  this  commissure  passes  between 
the  roof  nuclei,  there  decussating,  and  then,  taking  a  direct 
downward  course,  is  continuous  upon  each  side  with  the  vertical 
and  horizontal  branches  of  the  arbor  vitse.  According  to  Ober- 
stelner,  a  fasciculus  from  this  commissure  passes  between  the 
roof   nuclei,   there   decussating,  and   then   assuming  a   sagittal 

*  According  to  J.  S.  Risien  Russel,  the  direct  sensory  cerebellar  tract  of  Edinger  is  a  struc- 
ture entirely  separate  and  distinct  from  the  restiform  body,  and  ought  to  be  so  regarded. 
Anatomically  they  stand  out  clearly  and  distinctly  as  two  definite  structures,  having  little  if  any 
resemblance,  and  having  connections  totally  distinct  from  each  other.  Embryologically  it  has 
been  found  that  the  fibers  of  the  direct  sensory  cerebellar  tract  receive  their  myelin  at  a  dif- 
ferent period  to  the  fibers  of  the  restiform  body. 

f  According  to  von  Bechterew,  each  restiform  body,  or  inferior  cerebellar  peduncle,  con- 
tains a  tract  of  centripetal  or  afferent  fibers,  which  originate  from  cells  in  the  opposite  olivary 
body  and  terminate  chiefly  in  the  corpus  dentatum,  a  few  fibers  passing  to  the  cerebellar  cortex. 
Koelliker  states  that  no  such  afferent  cerebello-olivary  tract  exists,  the  olivary  fibers  being  the 
axones  of  the  cells  of  Purkinje  from  the  opposite  side. 


20S 


CENTRAL   NERVOUS  SYSTEM. 


course.  The  posterior  commissure  is  located  ventral  to  the 
fibers  of  the  corpora  dentata  and  is  continuous  on  each  side 
with  branches  of  the  arbor  vitae. 

A  system  of  short  fibers  of  association  connect  the  different 
cerebellar  folia;  they  are  located  just  beneath  the  cortex,  and  are 
called,  from  their  general  arrangement,  the  garland-like  fasciculi. 

The  fibers  of  the  before-mentioned  systems  may  be  divided. 


Fig.  104.— Schematic  Representation  of  the  Different  Constituents  of  the  Cor- 
tical Gray  Matter  of  the  Cerebellum. — [After  Van  Gehtuhten.') 

according  to  the  manner  in  which  impressions  are  conducted, 
into  two  sets — those  which  conduct  impressions  peripherally, 
and,  secondly,  those  which  conduct  them  centrally.  The  former 
fibers,  with  the  exception  of  those  which  pass  out  of  the  dentate 
bodies,  are  the  axones  from  the  cells  of  Purkinje.  The  latter  ter- 
minate, according  to  Cajal,  in  two  ways — first,  as  moss-like  fibers, 
so  called  because,  on  entering  the  granular  and  molecular  layers. 


THE   CEREBELLUM   OR    EPENCEPHALON.  209 

they  show,  in  their  course,  at  their  points  of  branching  and  at 
their  terminations,  irreo-ular,  moss-Uke  thickeningfs.  These 
fibers  terminate  mostly  about  the  cells  of  the  granular  layer ;  a 
few,  however,  end  in  the  molecular  layer.  The  second  set  of 
fibers  enter  the  molecular  layer  and  terminate  in  arborizations 
about  the  dendritic  ramifications  of  the  cells  of  Purkinje.  Ac- 
cording to  Koelliker,  however,  these  last-described  fibers  do  not 
terminate  about  the  cells  of  Purkinje,  but  about  the  basket  cells 
and  possibly  about  the  small,  stellate  cells  of  the  outer  mole- 
cular layer.  In  the  previous  description  of  the  cortex  of  the 
cerebellum,  it  was  described  as  consisting  of  two  layers — a  mole- 
cular and  a  granular.  However,  as  in  the  cerebral  cortex,  we 
find  in  the  cerebellum  five  distinct  layers  of  cortical  cells  :  First, 
the  small,  stellate  cells  ;  second,  the  large  cells  with  basket  ter- 
minations ;  third,  the  Purkinje  cells  ;  fourth,  the  small,  granular 
cells;  and,  lastly,  the  large,  granular  cells,  or  those  of  the  second 
type  of  Golgi.  All  of  these  cells,  save  those  of  the  third  layer, 
are  possibly  concerned  in  the  reception  and  conveyance  of  cen- 
tripetal sensory  impulses  to  the  cells  of  Purkinje.  The  latter 
are  supposedly  concerned  in  the  orderly  arrangement  of  such 
impulses,  and  in  originating  impulses  of  coordination  for  the 
maintenance  of  equilibrium.  This  connection  between  the  cells 
of  Purkinje  and  the  other  sets  of  cells  may  be  thus  explained. 
The  axones  of  the  small  granular  cells  form  horizontal  branches 
which  terminate  about  the  dendrites  of  the  cells  of  Purkinje, 
after  receiving  the  mosslike  terminals.  The  collaterals  of  the 
basket  cells  terminate  in  the  tuft-like  expansions  in  the  same 
way,  only  about  the  cell-bodies.  The  small,  stellate  cells,  owing 
to  their  connection  with  centripetal  fibers,  presumably  influence 
these  cells  in  the  same  manner.  The  collaterals  from  the 
axones  of  Purkinje's  cells  pass  upward,  and  probably  associate 
the  functions  of  many  Purkinje  cells.  The  action  of  the  large, 
granular  cells  is  thought  to  be  associate,  but  their  function  is 
not  definitely  known. 


14 


CHAPTER  V. 
THE  REGION  OF  THE  MID-BRAIN. 

From  the  middle  cerebral  vesicle  are  developed  the  parts 
which  afterward  form  the  mid-brain,  or  mesencephalon.  In 
adult  life  the  cavity  of  the  middle  cerebral  vesicle  has  become 
extremely  narrowed,  leaving  only  a  mere  channel  or  passage  of 
communication  between  the  third  ventricle  or  cavity  of  the 
primitive  fore-brain  and  the  fourth  ventricle  or  cavity  of  the 
hind-brain.  This  canal,  owing  to  this  fact,  is  often  called 
the  iter  a  tertio  ad  quartum  ventrlculum,  or  the  aqueduct 
of  Sylvius,  and  in  reality  forms  the  ventricle  of  the  mid-brain. 
It  is  about  two  centimeters  (nine  lines)  long,  is  lined  by  ciliated, 
columnar  epithelium,  which  is  surrounded  by  a  thick  layer  ol 
gray  matter,  continuous  with  that  of  the  fourth  ventricle.  On  trans- 
verse section  near  the  fourth  ventricle,  the  aqueduct  is  T-shaped, 
becomes  shield-shaped  until  near  the  third  ventricle,  when  it 
becomes  triangular.  Just  beneath  the  posterior  commissure  it 
expands  into  the  third  ventricle.  This  region  of  the  mid-brain 
is  a  means  of  connection  between  the  pons,  medulla,  and  cere- 
bellum below,  and  the  Inter-brain,  or  thalamencephalon,  and 
the  cerebral  hemispheres  above.  This  region  includes  the 
corpora  quadrigemina,  the  crura  cerebri,  the  Sylvian  aqueduct, 
and  adjoining  gray  matter  which  contains  the  nuclei  of  origin  of 
the  third  and  fourth  and  the  descending  root  of  the  fifth  pair 
of  cranial  nerves. 


THE  CORPORA  QUADRIGEMINA. 

The  corpora  quadrigemina  are  four  rounded  eminences  which 
are  developed  from  the  dorsal  wall  or  roof  of  the  mid-brain. 
They  are  separated  by  two  grooves,  a  median  longitudinal  and 


THE    REGION    OF   THE    MID-BRAIN.  211 

a  transverse,  the  latter  separating  them  into  a  ventral  or 
superior  pair  and  a  dorsal  or  inferior  pair.  The  former 
groove,  in  conjunction  with  the  transverse,  separates  them  from 
one  another.  They  are  located  just  behind  the  optic  thalami, 
third  ventricle,  and  posterior  commissure,  and  beneath  the  pos- 
terior extremity  of  the  corpus  callosum.  They  are  above  the 
crura  cerebri,  and  rest  upon  the  lamina  quadrigeminum,  beneath 
which  is  the  aqueduct  of  Sylvius.  The  anterior  or  superior 
pair,  much  the  larger,  are  termed  the  nates  ;  the  dorsal  or  inferior 
pair,  the  testes.    They  have,  extending  from  the  external  surface 


PULVINAR  OF  OPTIC 
THALAMUS 


CORPUS  GENICULATUM 
EXTERNUM 


CRUSTA 


'^Jr;^ PINEAL  BODl 

^ CORPUS  GENU 


PONS 


OLIVARY  BODY 


GENICULATUM 
INTERNUM 


CORPORA 
Q  UADRIGEMINA 


FILLET 


MIDDLE  CEREBELLAR 
PEDUNCLE 


—  INFERIOR  CEREBELLAR 
PEDUNCLE 


Pig.  105. — Lateral  View  of  Mesencephalon,  Pons,  and  Medulla. — [Gegenbaver.') 


of  each  side,  large  bundles  of  fibers,  termed  their  brachia,  or  arms, 
which  are  separated  by  a  groove  into  an  anterior  pair,  continu- 
ous with  the  anterior  corpora  quadrigemina,  and  a  posterior 
pair,  continuous  with  the  posterior  corpora.  The  brachium 
coming  from  the  side  of  each  anterior  corpus  passes  outward 
under  cover  of  the  pulvinar  of  the  optic  thalamus,  and  between 
it  and  the  internal  geniculate  body,  to  enter  the  external  gen- 
iculate body  and  the  optic  tract,  of  which  it  is  in  great  part  a 
prolongation.  The  posterior  brachia  are  very  short  and  divide 
into  two  fasciculi,  one  of  which  joins  the  internal  geniculate  body 


CENTRAL  NERVOUS  SYSTEM. 


and  the  other  disappears  beneath  that  body  and  probably  passes 
through  the  posterior  Umb  of  tlie  internal  capsule,  and  thence 
to  the  cortex  of  the  temporosphenoid  lobe. 


ANTERIOR  CORSr 

OF  LATERAL 

VENTRICLE 


FIFTH  VENTRICLE 

SEPTUM  L  UCID  UM 

ANTERIOR  PIT^ 

LARS  OF  FORNIX 

T.FNIA  SEMI- 

CIRCILARIS 

ASTER  [OR 

COMMISSI- RE 

THIRD  VENTRICLE 

MIDDLE 
COMMISSI' RE 

sricr's 

CIIOROIDEUS 

NA  TES 

CORPUS  GENICr- 
LA  TUM  INTERNUM 

LA  TERA  L  GROO  VE 

OF 
MESENCEPIIA  LON 
PONS 

CONDUCTOR 
SO  NOR  US 
SULCUS  LONGITUDINALIS 
MEDIAN  US 

TRIGONUM  HYPOGLOSSI 
CORPUS  RESTIFORME 

CLA  VA 
POSTERIOR  FISSURE 

SULCUS  PARAMEDIANUS 
DORS  A  LIS 

SULCUS  lA  TERALIS  DORSALIS 


CORPUS  CALLOSUM 


CA  UDA  TE 
NUCLEUS 


FORAMEN  OF 
MONRO 


OPTIC  THALAMUS 


STRIA  PIN EA  LIS 

PEDUNCULUS 
CONARII 

PINEAL  BODY 

SULCUS  CORP. 
QUAD.  LONGI- 
TUDINALIS 

TESTIS 

FRENULUM  VELI 
LING  ULA 

EMINENTIA  TERES 


TUBERCUIUM 
ACUSTICUM 


ALA  CINEREA 

TUBERCULUM  CUNEA TUM 
FUNICULUS  GRACILIS 
FUNICULUS  CUNEA  TUS 
LA  TERAL  COL  UMN 


Fig.  io6. — Metencephalon,  Mesencephalon,  and  THAi.AMENCEPfrALON,  from  the 
Dorsal  Surface. — {Afte7-  Obersteiner.) 


MINUTE  ANATOMY. 

If  a  transverse  section  be  made  through  the  anterior  or  supe- 
rior corpora  quadrigemina  of  any  mammal,  the  naked  eye  will 
discern  that  the  gray  and  the  white  matter  composing  them  are 
arranged  in  successive  layers.      If  the  section  then  be  observed 


THE   REGION   OF   THE   MID-BRAIN.  213 

with  a  low  power  of  the  microscope,  six  distinct  layers  can  be 
recognized — viz.  : 

First,  a  narrow,  outer  layer,  consisting  of  neuroglia  cells  and 
fibers,  the  cells  being  of  the  stellate  variety. 

Second,  a  superficial  layer  of  medullated  nerve-fibers,  forming 
a  stratum  zonale,  they  being  composed  almost  entirely  of  fibers 
from  the  optic  tract,  which  are  the  axones  from  the  multipolar 
cells  of  the  retina,  they  arborize  about  the  dendrites  of  the  cells 
of  the  underlying  third  layer. 


.4f 


Fig.  107. — MicROPHOTOGRAPii  OF  A  Transverse  Section  Through  the  Corpora  Quad- 
RIGEMINA  of  A  Sheep.      Showing  layer  of  superficial  cells.      Method  of  Berkley. 

Third,  a  superficial  layer  of  gray  matter,  consisting  of  an 
outer,  lighter-colored  portion  of  optic  fibers  and  an  inner,  dark 
portion  about  which  these  fibers  end.  There  are  two  chief 
forms  of  cells  in  this  superficial  gray  layer — an  outer  layer  of 
spindle-cells,  and  an  inner  layer  of  small,  polygonal  cells.  Some 
of  the  former  resemble  the  small,  pyramidal  cells  of  the  second 
layer  of  the  cerebral  cortex.  In  the  sheep  these  cells  fre- 
quently give  off  four  dendrites,  two  basal  and  two  apical,  the 


214  CENTRAL  NERVOUS  SYSTEM. 

former  being  sliort,  seldom  branching,  and  are  finer  than  the 
latter.  The  apical  dendrites  continue  upward  until  they  reach 
the  layer  of  superficial,  medullated  fibers,  where  they  frequently 
bifurcate,  ending  free  or  in  a  roundish  swelling.  Many  of  them 
have  but  one  apical  dendrite,  which  is  thick  and  forks  after  a 
short  course,  each  branch  proceeding  to  the  superficial  layer 
and  ending  free. 

All  these  dendrites  possess  tuberous  excrescences,  which  give 
a  peculiar,  beaded  appearance  to  the  layer.  Their  axones  are 
difficult  to  follow,  owing  to  the  tangle  of  fibers  occurring  in  this 
layer.  Most  of  them  come  from  the  base  of  the  cell-body,  while 
some  are  given  off  from  the  main  apical  dendrite.  They  course 
forward  and  outward  toward  the  optic  fibers.  The  small,  tri- 
angular or  polygonal  cells  possess  from  two  to  four  dendrites, 
which  come  ofT  from  angles  of  the  cell-body.  These  branches 
are  moderately  thick,  pursue  mostly  an  oblique  or  a  horizontal 
course,  branch  frequently  at  a  distance  from  the  cell-body,  and 
terminate  in  free  ends  about  cells  of  a  like  nature.  Starr  states 
that  the  axones  of  these  cells  enter  the  optic  tract  and  pass  to 
the  occipital  cortex. 

The  fourth  layer  consists  of  inner  medullated  nerve-fibers, 
which  have  a  longitudinal  course,  and  enter  both  the  superficial 
and  deep  layers  of  gray  matter.  This  layer  contains  axones 
from  the  cells  of  the  outer  gray  layer,  passing  to  the  occipital 
cortex,  to  end  about  the  pyramidal  cells  there,  and  axones  pass- 
ing in  an  opposite  direction  from  the  occipital  cortex  to  the 
outer  gray  layer  previously  described  (von  Monakow). 

The  fifth  or  deep  layer  of  gray  matter  contains  a  number  of 
large,  multipolar,  triangular  and  polygonal  cells,  resembling 
closely  the  cells  of  the  anterior  cornua  of  the  spinal  cord,  poss- 
essing from  two  to  six  very  stout  and  long  dendrites,  which 
become  attenuated  in  their  course,  branch  frequently,  and  ter- 
minate free  in  a  Y-shaped  end.  The  axones  come  off  usually 
from  the  base  of  the  cell,  or  from  one  of  the  main  dendrites, 
and  have  a  mesial  or  dorsal  course  toward  the  fillet.  Some  of 
them  probably  pass  to  the  red  nucleus  and  to  the  nucleus  of  the 
oculomotor  nerves. 

The   sixth    layer   consists   of    the    central  gray  matter    sur- 


Fig.  io8.— a  Characteristic  Cell  from-the  Third  (Gray)  Layer  of  the  Optic  Lobe 
OF  AN  Eighteen-day-old  Chicken.     Golgi's  method. — {After  Koelliker.) 

N.   The  neuraxone  from  the  cell-body  with  its  numerous  collaterals. 

215 


d'-- 


/ 


C.O.T. 


Fig.  109. — Schematic  Representation  of  the  Essential  Histologic  Elements  of 
THE  Optic  Lobe  of  a  Bird.  Showing  the  probable  route  taken  by  visual  impressions 
to  reach  the  cerebral  (occipital)  cortex. — [After  KoelUker.) 

C.R.F.  Centripetal  retinal  fibers  with  terminal  arborizations,  ^,  ^,  f.  aswAsp.c.  Spindle-shaped 
cells  of  the  second  layer  with  descending  axones.  b.  Pyramidal-shaped  cell  of  the  third 
layer  with  a  descending  axone  coming  from  the  chief  apical  dendrite,  c,  c.  Triangular- 
shaped  cells  also  with  descending  axones.  The  axones  from  the  above-named  cells  form 
C.O.T.,orthe  cerebral  optic  tract,  d.  Spindle-shaped  cell  of  third  layer  whose  axone 
ascends  and  forms  a  centrifugal  optic  fiber  which  probably  terminates  in  the  retina. 

217 


THE   REGION   OF   THE   MID-BRAIN. 


219 


rounding  the  aqueduct  of  Sylvius.  It  is  from  two  to  three 
millimeters  thick,  and  is  composed  of  a  homogeneous  mass  of 
neuroglia  tissue,  chiefly  made  up  of  spheric  or  slightly  oblong 
neuroglia  cells,  with  innumerable  long,  slender  processes  radi- 
ating from  all  parts  of  the  cell-body.  Embedded  in  this  neuroglia 
mass  exists  a  number  of  small  and  large  multipolar  nerve-cells, 
the  small  cells,  triangular  in  shape,  being  scattered  throughout 
the  inner  portion  of  the  neuroglia  layer,  and  each  possessing 
four  to  eisfht  dendrites  and  a  fine  long-  neuraxone,  whose  course 
is  ventrolateral  or  mesial.  The  collaterals  from  these  axones 
form  the  arch-like  fibers  of  this  layer.     The  large  cells  belong 


Fig.  iio. — Transverse  Section  Through  the  Corpora  Quadrigemina  from  an  Eight- 
months'  Human  Fetus. — (After  KoelUker.) 
In  the  region  of  the  aqueduct  of  Sylvius  and  between  the  arching  fibers  are  to  be  seen  the  char- 
acteristic  nauUipolar  cells  of  the  gray  matter  of  this  region. 

to  the  nuclei  of  origin  of  the  third,  fourth,  and  upper  or  descend- 
ing root  of  the  fifth  nerve.  They  are  located  ventral  to  and  on 
each  side  of  the  aqueduct  of  Sylvius  (Fig.  no). 

The  posterior  quadrigeminal  bodies  possess  small  (15  to 
20  //-)  and  large  {y::>  to  50  /-/)  multipolar  nerve-cells,  similar  to 
those  which  exist  in  the  anterior  corpora  quadrigemina.  The 
course  of  their  axones  is  dorsal,  mesial,  or  lateral,  and  they  prob- 
ably enter  the  lateral  fillet  or  lemniscus  or  the  posterior  brachia. 
The  cells  of  the  posterior  corpora  quadrigemina  are  connected 
with  the  auditory  apparatus  by  means  of  the  lateral  fillet,  the 
fibers  of  which  end  in   part  about  these  cells,  and  in  part  about 


220  CENTRAL  NERVOUS  SYSTEM. 

the  cells  of  the  lateral  tegmental  nucleus.  From  these  cells 
new  axones  start  out  and,  entering-  the  posterior  brachium, 
radiate,  after  passing  through  the  extreme  posterior  end  of  the 
internal  capsule,  through  the  centrum  ovale,  terminating  about 
the  cells  of  the  first  and  second  temporosphenoid  lobes.  The 
axones  of  the  cortical  cells  of  the  temporosphenoid  lobe  pass 
centrifugally  via  the  posterior  brachium,  and  end  about  the  cells 
of  the  posterior  corpora  quadrigemina,  thus  forming  a  double 
connection  between  these  bodies  and  the  cortex  of  the  temporo- 
sphenoid lobe. 


THE  CEREBRAL  PEDUNCLES. 

These  peduncles,  or  crura  cerebri,  consist  chiefly  of  longi- 
tudinal tracts  or  fasciculi  of  fibers  which  have  both  a  cen- 
trifugal and  a  centripetal  course.  They  serve  to  connect 
the  cerebral  cortex  and  basal  ganglia  with  the  pons,  medulla, 
cerebellum,  and  the  spinal  cord.  Each  peduncle  is  separated 
into  a  ventral  convex  portion,  called  the  crusta,  or  "Fuss" 
(German),  and  a  dorsal,  slightly  concave  portion,  the  teg- 
mentum, by  the  crescentic  gray  area  of  dark  pigmented  nerve- 
cells,  the  substantia  nigra,  which  area  extends  from  the  upper 
margin  of  the  pons  Varolii  to  the  posterior  border  of  the 
corpora  mammillaria,  and  reaches  the  surface  on  both  the 
inner  and  outer  sides  of  the  peduncle.  On  its  inner  side  is 
a  groove,  the  sulcus  oculomotorius,  through  which  passes  the 
third  nerve.  On  the  outer  side  another  groove  exists — the 
sulcus  lateralis. 

The  ventral  portion  or  crusta,  also  called  pes  pedunculi,  con- 
sists of  the  following  systems  of  longitudinal  fibers:  First,  the 
motor  or  pyramidal  tract ;  second,  a  tract  connecting  the  tem- 
poral and  occipital  lobes  with  the  pons,  and  thence  with  the 
opposite  cerebellar  hemisphere  ;  third,  the  frontocerebellar  tract ; 
fourth,  a  fasciculus  of  fibers  located  above  the  pyramidal  tract, 
between  it  and  the  substantia  nigra  ;  fifth,  a  small  bundle  of 
fibers  on  the  inner  side  of  the  crusta,  joining  the  fillet. 

First,  the  pyramidal  or  motor  tract  of  each  side  forms  in  the 
medulla  the  anterior  pyramids,  which,  on  reaching  the  inferior 


THE    REGION   OF    THE    MID-BRAIN.  221 

border  of  the  pons,  separate  into  distinct  bundles  which  He 
between  the  superficial  and  deep  transverse  pontine  fibers.  On 
emerging  from  the  superior  border  of  the  pons  they  are  again 
collected  into  two  bundles,  which  occupy  the  middle  two-fifths 
of  each  crus.  They  then  course  upward  until  they  reach  the 
internal  capsule,  where  they  form  the  anterior  two-thirds  of  the 
posterior  limb  of  the  internal  capsule,  and  radiate  to  the  region 
about  the  fissure  of  Rolando,  known  as  the  motor  area  of  the 
cerebral  cortex.     The  reason  for  tracing  the  course  of  the  motor 


Fig.   hi. — Transverse  Section  Through  the  Mid-brain  of  an  Adult.     Weigert's 

method. 
•A.C.Q.  Anterior  corpus  quadrigeminum.  A.S.  Aqueduct  of  Sylvius.  C.G.M.  Central  gray 
matter.  F. D.O.T.  Fountain-like  decussation  of  tegmentum  (Meynert's).  L. F.  Lateral 
fillet  or  lemniscus.  M.F.  Mesial  fillet  or  lemniscus.  III.  Root-fibers  of  the  third 
(oculomotor)  nerves.  R.N.  Red  or  tegmental  nucleus.  P.  Pulvinar  of  optic  thalamus. 
S.N.  Substantia  nigra.     P.P.   Pes  pedunculi  or  cerebral  peduncles. 


tract  in  a  direction  opposite  to  the  development  and  conduction 
of  its  component  fibers  is  given,  on  page  141,  section  Medulla 
Oblongata. 

The  second  is  a  tract  which  connects  the  occipital  and  temporal 
lobes  with  both  cerebellar  hemispheres,  but  chiefly  with  the  one 
of  the  opposite  side.  The  fibers  of  this  tract  proceed  from  the 
pyramidal  cells  of  the  cortex  of  the  occipital  and  temporal  lobes. 
The  tract  passes  beneath  the  lenticular  nucleus,  and  between  its 
posterior  extremity  and  the  external  geniculate  body,  and  forms  a 


222  CENTRAL  NERVOUS  SYSTEM. 

fasciculus  which  continues  downward  in  the  outer  side  of  the 
crusta,  occupying  about  one-fifth  of  its  bulk.  It  extends  into 
the  pons,  where  the  individual  fibers  arborize  about  the  cells  of 
the  nucleus  pontis,  which  nucleus  continues  this  tract,  by  way  of 
the  middle  cerebellar  peduncle,  to  both  cerebellar  hemispheres, 
but  chiefiy  to  that  of  the  opposite  side. 

Third,  the  frontocej^ebellar  tract  occupies  rather  more  than 
the  inner  fifth  of  the  crusta.  The  fibers  of  this  tract  come  from 
the  prefrontal  lobe,  and  pass  between  the  lenticular  and  cau- 
date nuclei,  occupying  a  large  part  of  the  anterior  limb  of  the 


Fig.  112. — Diagram  of  Section  of  the  Crus. — {Modified frovi  Wernicke,  from  Cowers.) 
LF,  UF.  Upper  and  lower  fillet.  C  Q  A.  Anterior  corpora  quadrigemina.  Aq.  Aqueduct. 
III.  Nucleus  of  third  nerve  (3).  P  H.  Posterior  horizontal  fibers,  c  p.  Brachium  of  the 
posterior  corpora  quadrigemina.  R  N.  Red  nucleus.  S  N.  Substantia  nigra.  CGI. 
Internal  geniculate  body.  T  O  C.  Temporo-occipital  cerebellar  fibers.  Py.  Pyramidal 
fibers.  F  C.  Frontocereljellar  libers.  C  C.  Caudate  cerebellar  fibers,  t.  Inner  fibers  of 
crusta  to  tegmentum. 

internal  capsule,  and  course  downward  on  the  inner  side  of 
the  pyramidal  tract,  ending  in  the  ventral  portion  of  the  pons 
Varolii  about  the  nerve-cells  of  the  nucleus  pontis  of  the  same 
side.  The  cells  of  the  nucleus  pontis  of  each  side  are  joined  by 
fibers  from  the  cortex  of  both  cerebellar  hemispheres,  chiefly, 
however,  with  the  cerebellar  hemisphere  of  the  opposite  side. 
The  fibers  are  the  axones  of  the  cells  of  Purkinje  of  the  same 
and  the  opposite  side,  the  latter  fibers  having  crossed  in  the 
raphe,  thus  establishing  a  connection  between  the  frontal  lobe  of 
one  side  and  both  cerebellar  hemispheres,  but  chiefly  with  the 
cerebellar  hemisphere  of  the  opposite  side. 


THE   REGION   OF    THE   MID-BRAIN.  223 

Fourth,  a  rather  broad  but  thin  layer  of  fibers,  which  in  the 
crusta  is  located  above  the  pyramidal  tract,  and  between  it  and 
the  substantia  nigra.  This  bundle  of  fibers,  according  to  Flech- 
sig,  arises  from  the  cells  of  the  corpus  striatum,  and  continues 
downward  through  the  crusta  to  the  cells  of  the  nucleus  pontis. 
These  latter  cells  may  continue  this  tract  by  their  axones  to  the 
cortex  of  the  same  and  opposite  cerebellar  hemisphere,  establish- 
ing a  cross-connection  between  the  corpus  striatum  of  one  side 
and  the  cerebellar  hemisphere  of  the  same  and  the  opposite  side. 

Fifth,  the  small  bundle  of  fibers  which  occupies  the  most  mesial 
portion  of  the  ci^ttsta  is  said  to  join  the  fillet.  According  to 
Spitzka,  this  bundle  of  fibers  contains  the  central  sensory  tracts 
for  the  cranial  nerves. 

The  tegmentum  or  dorsal  part  of  the  crura  cerebri  is  con- 
tinuous anteriorly  with  the  tegmental  region  beneath  the  optic 
thalami,  and  below  with  the  tegmental  region  of  the  pons  and 
medulla.  It  contains  longitudinal  tracts  of  fibers, — continuations 
of  tracts  proceeding  upward  from  the  medulla,  cerebellum,  and 
pons, — in  addition  to  several  fasciculi  of  arched  fibers,  having 
among  them  several  scattered  collections  of  gray  matter.  The 
tegmentum  is  divided  into  a  right  and  a  left  half  by  the  upward 
continuation  of  the  raphe,  at  which  point  the  various  decussa- 
tions take  place.  The  following  longitudinal  tracts  of  fibers 
are  to  be  found  in  the  tegmentum  :  First,  the  mesial  fillet,  or 
mesial  lemniscus  ;  second,  the  lateral  fillet,  or  lateral  lemniscus  ; 
third,  the  superior  cerebellar  peduncles  ;  fourth,  the  superior  lon- 
gitudinal bundles  ;  fifth,  the  remaining  longitudinal  tracts  of  the 
formatio  reticularis.  It  will  be  proper  at  this  point  to  trace  these 
various  systems  of  fibers  not  only  through  the  tegmentum  of 
each  crus,  but  to  their  termination,  either  in  the  basal  ganglia 
or  in  the  cerebral  cortex  (Figs.  1 1 1  and  112), 


THE  MESIAL  FILLET,  OR  LEMNISCUS. 

This  is  a  continuation  brainward  of  the  axones  of  the  cells  of 
the  nucleus  gracilis  and  nucleus  cuneatus.  In  describing  the 
course  of  the  long  tracts  of  fibers  in  the  posterior  columns  of 
the  cord,  it  was   found  that  they  terminated  about  the  cells  of 


224  CENTRAL  NERVOUS  SYSTEM. 

the  previously-mentioned  nuclei,  and  that  most  of  the  axones  of 
these  cells  on  each  side  passed  ventromesially  as  internal 
arcuate  fibers  to  decussate  in  the  raphe  between  the  olivary 
bodies,  forming"  the  so-called  interolivary  or  superior  sensory 
decussation.  They  then  continue  their  course  just  back  of  the 
anterior  pyramid  of  the  opposite  side  in  the  same  relative  posi- 
tion through  the  pons,  occupying  the  ventral  portion  of  the 
formatio  reticularis.  On  transverse  section,  each  mesial  fillet 
forms  an  oblong  area  on  both  sides  of  the  raphe,  just  dorsal  to 
the  deep,  transverse,  pontine  fibers.  In  the  crus  it  occupies  the 
ventral  portion  of  the  tegmentum,  and  becomes  continuous  lat- 
terly with  the  lateral  fillet,  or  lateral  lemniscus,  which  here  occu- 
pies a  somewhat  triangular  area  in  the  outer  side  of  the  tegmen- 
tum, the  two  thus  forming  a  sickel  or  crescentic  mass  of  fibers. 
On  its  course  brain  ward  the  mesial  fillet  receives  an  accession 
of  fibers  from  the  anterolateral  columns  and  from  the  cells  of 
the  various  end  nuclei  of  the  sensory  cranial  nerves  of  the 
opposite  side,  save  the  auditory,  forming  for  those  nerves  cen- 
tral, sensory  tracts.  The  mesial  fillet  gives  off  both  axones  and 
collaterals  to  the  cells  of  both  the  median  and  lateral  fields 
of  the  formatio  reticularis. 

The  mesial  fillet  then  continues  brainward  in  the  teo-mentum 
of  the  crus  to  the  subthalamic  region,  where,  accordinof  to 
Bechterew^  the  fibers  from  the  cells  of  the  nucleus  gracilis,  and 
those  from  the  nucleus  cuneatus,  pursue  different  courses. 
Some  fibers  from  the  cuneate  nucleus  pass  to  the  anterior 
corpus  quadrigeminum,  giving  off  on  their  way  a  few  fibers  and 
collaterals  to  the  nucleus  of  the  lateral  fillet,  or  lemniscus.  The 
main  bundle,  however,  continues  upward  to  the  outer  side  of 
Luy's  body,  to  form  two  fasciculi,  one  joining  the  lenticular 
loop  and  the  other  Meynert's  commissure. 

The  first  of  these  fasciculi  passes  to  the  globus  pallidus  of  the 
lenticular  nucleus  of  the  same  side,  while  the  remaining  fascic- 
ulus passes  to  the  lenticular  nucleus  of  the  opposite  side  by 
way  of  Meynert's  commissure.  The  fibers  of  both  fasciculi  end 
about  the  intrinsic  cells  of  these  nuclei,  whence  new^  axones  start 
out  and  radiate  to  the  cortex  of  the  central  and  parietal  convolu- 
tions, thus  establishinor  a  connection  between  the  nucleus  cuneatus 


Fig. 


113. — Diagram  Indicating  the  Course  of  the  Motor  and  Sensory  Fibers 
OF  the  Spinal  Cord  and  Medulla. 


.  Motor  cells  of  the  ceiebral  cortex,  b,  b.  Arborizations  of  the  fibers  of  the  sensory  tract 
in  the  cerebral  cortex,  c.  Nucleus  of  the  column  of  Burdach,  showing  terminal  arboriza- 
tions of  the  long  sensory  fibers  of  the  cord.  d.  Nucleus  of  the  column  of  GoU,  showing 
terminal  arborizations  of  the  long  sensory  fibers  of  the  cord.  e.  Section  of  the  medulla, 
showing  sensory  decussation,  f.  Section  of  medulla,  showing  motor  or  pyramidal  decus- 
sation, g,  g.  Motorial  end  plates,  h.  Section  through  the  cervical  region  of  the  cord, 
showing  termination  in  the  anterior  horn  of  the  motor  fibers  of  the  direct  pyramidal  tract 
after  they  have  crossed  in  the  anterior  commissure  ;  also  fiber  of  crossed  pyramidal  tract  end- 
ing about  anterior  horn  cell  of  same  side.  i,i.  Posterior  spinal  ganglia.  j,k.  Sensory  fibers 
of  short  course.  /.  Sensory  fibers  of  long  course,  terminating  in  medulla,  w,  m,  m.  Sen- 
sory end  organs,      n.   Section  through  lumbar  cord. 

15  225 


THE   REGION   OF    THE   MID-BRAIN. 


227 


and  the  cortex  of  the  central  and  parietal  lobes.  The  portion  of 
the  fillet  whose  fibers  are  the  axones  of  the  cells  of  the  nucleus 
gracilis  course  mesially  to  the  fibers  from  the  nucleus  cuneatus,and 
give  off  collaterals  which  join  the  anterior  corpus  quadrigeminum, 
ending  probably  about  the  cells  of  the  fifth  layer.  The  main 
bundle  of  fibers  continues  forward  to  end,  according  to  von  Mon- 


LM 


LM 


Fig.  114. — Transverse  Section  Through  the  Spinal  End  of  the  Posterior  Cor- 
pora QUADRIGEMINA  OF  A  CAT.     V/eigert  preparation. — {After  Koelliker.) 

Be.  Brachium  conjunctivum  (superior  cerebellar  peduncle).  C.  Commissure.  Fid.  Posterior 
longitudinal  bundle.  G.  Fibers  from  lateral  fillet  passing  medianward  as  fibrse  arcuatse. 
LI.  Fibers  of  the  lateral  fillet  or  lemniscus  terminating  about  the  cells  of  the  posterior  corpus 
quadrigeminum.  LM,  LM.  Median  fillet  or  lemniscus.  Nqd.  Nucleus  of  the  posterior 
corpus  quadrigeminum.  P.  Superficial  pons  fibers,  /^t.  Pyramidal  bundles  of  fibers. 
R.    Raphe.      Sr.    Substantia  reticularis.      A.   Aqueduct  of  Sylvius. 


akow,  Schlesinger,  and  Mott,  about  the  cells  of  the  ventral 
nucleus  of  the  optic  thalamus,  where,  by  means  of  the  axones 
from  the  cells  of  this  nucleus,  this  tract,  now  called  the  cortical 
fillet,  is  further  continued  through  the  posterior  division  of  the 
internal  capsule,  and  through  the  centrum  semiovale,  to  termi- 
nate in  the  region  of  the  central  convolutions,  chiefly  the  post- 
central and  parietal  gyri.     The  mesial  fillet  contains  a  tract  of 


228  CENTRAL.  NERVOUS  SYSTEM. 

fibers  which  have  been  found  to  degenerate  downward  after 
lesions  of  the  central  ganglia,  especially  after  destruction  of  the 
optic  thalamus ;  this  degeneration  extends  downward  toward  the 
nuclei  of  the  posterior  columns*  (Figs,  i  i  i.  112,  and  i  13). 

The  lateral  fillet,  or  lateral  lemniscus,  is  the  chief  central 
auditory  tract.  It  forms  an  area  somewhat  triangular  on  the 
outer  side  of  the  pons.  It  is  composed,  first,  of  axones  from  the 
cells  of  the  ventral  auditory  nucleus,  chiefly  of  the  opposite  side  ; 
second,  axones  from  the  cells  of  the  ventral  auditory  nucleus,  pass- 
ing dorsally  around  the  restiform  body  and  beneath  the  ependyma 
of  the  fourth  ventricle  (striae  acoustical),  decussating  with  their 
fellows  in  the  raphe,  and  proceeding  ventrolaterally  to  join  the 
lateral  fillet  of  the  opposite  side,  a  few  fibers  passing  without 
decussating  into  the  lateral  fillet  of  the  same  side  ;  third,  axones 
from  the  cells  of  the  superior  olivary  body,  which,  after  decus- 
sating in  the  raphe,  pass  to  the  opposite  lateral  fillet,  a  few  fibers 
passing  to  the  lateral  fillet  of  the  same  side  ;  fourth,  axones 
from  the  cells  of  the  nucleus  of  the  lateral  fillet ;  fifth,  fibers  joining 
the  lateral  fillet  in  the  region  of  the  corpora  quadrigemina.  which 
come  from  the  ventral  tegmental  decussation.  The  lateral  fillet 
occupies,  in  the  ventrolateral  part  of  the  tegmentum  of  the  crus, 
a  trianorular  area  which  is  continuous  on  the  inner  side  with  the 
mesial  fillet.  It  continues  brainward  in  the  same  position  until 
it  reaches  the  region  of  the  posterior  corpus  quadrigeminum, 
where  most  of  the  fibers  terminate  about  its  cells,  while  some 
terminate  about  the  cells  of  the  internal  geniculate  body  and 
posterior  nucleus  of  the  optic  thalamus.  According  to  Koel- 
liker,  some  of  the  fibers  terminate  also  about  the  cells  of  the 
upper  portion  of  the  lateral  nucleus  of  the  lemniscus.  A  small 
bundle  of  fibers  from  the  lateral  fillet  ends  about  the  cells  of  the 
anterior  corpus  quadrigeminum,  some  axones  of  which  are  con- 
nected with  the  nuclei  of  the  third  and  fourth  nerves,  and 
whose  cells  are  also  connected  with  the  terminal  fibers  of  the 
optic  nerve.  This  connection  may  serve  a  common  reflex  pur- 
pose, by  means  of  which  movements  of  the  eyeballs  may  be 
excited,  owing  to  auditory  or  optic  impressions. 

* -Such  cases  have  been  recorded  by  Bruce,  Campbell,  Jacob,  and  Mahaim. 


THE    REGION   OF    THE    MID-BRAIN. 


229 


From  the  cells  of  the  posterior  corpora  quadrigemina,  internal 
geniculate  body,  and  posterior  nucleus  of  the  optic  thalamus, 
axones  pass  out  by  way  of  the  posterior  arm,  or  brachium, 
through  the  extreme  posterior  end  of  the  internal  capsule,  and 
thence  radiate  through  the  centrum  semiovale  to  the  pyramidal 
cells  of  the  superior  and  middle  temporosphenoid  lobes. 


Fig.  115. — Horizontal  Section  Through  the  Cerebellum. 
A.C.Q.  Anterior  corpora  quadrigemina.     P.C.Q.    Posterior  corpora  quadregemina.      CD.  Cor- 
pus den  tatum.      M.C.P.   Middle  cerebellar  peduncle.    S.C.P.   Superior  cerebellar  peduncle. 
I.e. P.    Inferior  cerebellar    peduncle.      F.V.  Fourth  ventricle. 


THE  SUPERIOR  CEREBELLAR  PEDUNCLES. 

The  centripetal  fibers,  of  which  each  peduncle  is  composed, 
have  their  chief  origin  from  the  cells  of  the  dentate  nucleus  of 
the  cerebellum.  A  few  centripetal  fibers  join  the  peduncles 
from  the  cortex  of  the  worm,  being  the  axis-cylinders  from  the 
cells  of  Purkinje.  These  peduncles  make  two  compact  bundles, 
one  on  each  side  of  the  upper  part  of  the  fourth  ventricle,  form- 
ing its  outer  boundaries,  and  having  between  them  the  superior 
medullary  velum.  In  their  course  brainward  they  converge  and 
become  located  in  the  roof  of  the  fourth  ventricle  and  on  each 
side    of  the   aqueduct  of  Sylvius,   where    they    form  two    long 


2^0  CENTRAL   NERVOUS  SYSTEM. 

bundles  of  fibers,  crescentic  on  transverse  section,  which  occupy 
a  large  part  of  the  dorsolateral  periphery  of  the  tegmentum. 
As  they  approach  the  region  of  the  posterior  corpora  quadri- 
gemina  they  are  more  ventrally  located,  just  posterior  to  the 
red  or  tegmental  nuclei  ;  the  greater  part  of  the  fibers  of  each 
bundle  decussate  with  their  fellows  of  the  opposite  side,  and  ter- 
minate about  the  cells  of  the  posterior  portion  of  the  nucleus 
ruber  of  the  opposite  side.  A  number  of  fibers  do  not  decus- 
sate, but  pass  to  the  nucleus  ruber  of  the  same  side.  Some  of 
the  fibers  of  the  superior  cerebellar  peduncles  pass  through  the 
nuclei  rubri  into  the  optic  thalami,  where  they  terminate.  Many 
fibers,  probably  axones  from  the  cells  of  the  nucleus  ruber,  con- 
tinue onward  to  end  about  the  ventral  portion  of  the  optic  thal- 
amus, from  the  cells  of  which  new  fibers  start  out  to  pass  through 
the  posterior  portion  of  the  internal  capsule,  and  thence  radiate 
to  the  region  of  the  central  gyri  and  parietal  lobe.  Some  of 
these  fibers  may  terminate  in  the  lenticular  nucleus.  Some 
anatomists  do  not  agree  with  this  description  of  the  cortical 
termination  of  this  tract.  There  is  also  included  in  each  superior 
cerebellar  peduncle  a  centrifugal  tract  of  fibers,  which  arises  from 
the  cells  of  the  opposite  red  nucleus,  and  probably  terminates 
amoncT  the  cells  of  the  dentate  nucleus  of  the  cerebellum. 


THE   SUPERIOR  LONGITUDINAL  BUNDLE. 

Each  bundle  appears  on  cross-section  as  a  somewhat  triangular- 
shaped  area  of  longitudinal  fibers,  located  on  one  side  of  the 
raphe  beneath  the  gray  matter  of  the  fourth  ventricle  and  that 
of  the  aqueduct  of  Sylvius.  F^ach  bundle  extends  upward  to  a 
collection  of  cells  in  the  central  gray  matter  of  the  third  ventricle, 
at  the  beginning  of  the  aqueduct  of  Sylvius  and  ventral  to  the 
oculomotor  nucleus.  This  is  Edinger's  nucleus,  or  the  nucleus 
of  the  posterior  longitudinal  bundle,  where,  according  to  Cajal, 
a  large  part  of  the  fibers  terminate,  the  rest  continuing  onward 
to  end  in  the  optic  thalamus.  Inferiorly,  they  are  continuous 
with  the  fibers  of  the  anterior  ground  bundles  of  the  spinal  cord, 
being,  in  reality,  their  upward  extensions.  In  the  medulla, 
owing  to  the  motor  and  sensory  decussations  and  the  interposi- 


Fig.  ii6. — Microphotograph  Through  the  Red  Nuclei  of  the  Mid-brain  of  a 
Young  Sheep.  Showing  decussation  of  the  fibers  of  the  superior  cerebellar  peduncles. 
Method  of  Golgi. 


Fig.  117. — Microphotograph  of  a  Section  through  the  Red   or   Tegmental   Nu- 
cleus OF  A  Young  Sheep.     Showing  seven  of  its  characteristic  cells,     Golgi  method. 

231 


THE   REGION   OF    THE   MID-BRAIN.  233 

tion  of  many  fibers  and  cells,  these  ground  bundles  become  dis- 
placed dorsally,  and  come  to  occupy  a  position  on  each  side  of 
the  raphe,  in  the  dorsal  part  of  the  formatio  reticularis.  In  their 
course  the  posterior  long-itudinal  bundles  of  fibers  give  off  col- 
laterals to  the  motor  nerves  concerned  in  the  movements  of  the 
eyeballs  (III,  IV,  and  VI),  and  probably  to  all  the  motor  cranial 
nerves.  These  collaterals  pass  in  the  raphe  to  the  nuclei  of  the 
opposite  side,  although  a  few  pass  to  the  nuclei  of  the  same 
side.  It  is  probable  that  collaterals  and  axones  from  these 
bundles  also  terminate  about  the  cells  of  the  substantia  reticu- 
laris grisea.  According  to  Cajal,  the  posterior  longitudinal 
bundle  of  fibers  receives  accessions  of  fibers  from  the  auditory 
nucleus  of  Deiter,  which  have  an  ascendinsf  course  and  orive  off 
numerous  collaterals  to  the  motor  nerves  of  the  eyeballs,  and, 
secondly,  from  the  sensory  trigeminal  nuclei,  and  from  the  cells 
of  the  formatio  reticularis  alba. 

Despite  much  clinical  and  experimental  research,  doubt  still 
exists  with  regard  to  the  exact  course  and  termination  of  the 
two  remaining  tracts  of  the  formatio  reticularis — namely,  the 
anterolateral  ascending  tract  of  Cowers  and  Bechterew  and  the 
lateral  ground  bundle  of  fibers.  The  former,  which  occupies,  in 
the  cord,  a  triangular  or  broadly  comma-shaped  area  along  its 
anterolateral  periphery,  ventral  to  the  direct  cerebellar  and 
cross-pyramidal  tracts,  ascends  to  the  medulla,  where,  according 
to  Gowers  and  Bechterew,  the  fibers  may  be,  in  part  or  totally, 
intercepted  by  the  cells  of  the  lateral  nucleus,  and  the  tract  is 
further  continued,  by  means  of  the  axones  from  these  latter  cells, 
which  enter  the  lateral  field  of  the  formatio  reticularis,  occupying 
a  position  in  the  medulla  dorsolateral  to  the  lower  olivary  body, 
and  continuing  in  the  same  relative  position  through  the  pons 
and  brain-stem,  to  pass  with  the  fibers  of  the  mesial  fillet  through 
the  posterior  division  of  the  internal  capsule,  and  radiating 
through  the  centrum  ovale,  to  terminate  in  the  cortex  of  the 
parietal  lobe.  On  the  other  hand,  the  studies  of  Auerbach, 
Lowenthal,  and  Patrick  on  lower  animals,  and  of  Hoche  in 
man,  would  seem  to  prove  that  this  tract,  after  reaching  the 
pons,  passes  into  the  cerebellum. 

In  the  description  of  Gowers'   tract,  contained  in   the   section 


234  CENTRAL  NERVOUS  SYSTEM. 

on  the  spinal  cord,  the  termination  of  tlie  tract  was  given  ac- 
cording to  the  latest  view  advanced  by  Hoche.  hroni  a  clinical 
standpoint,  however,  this  description  seems  inadequate,  because 
lesions  of  the  parietal  cortex  have  been  followed  by  a  loss 
of  sensation  of  temperature  and  pain.  Therefore,  if  we  must 
assume  that  Gowers'  tract  conducts  such  sensations,  a  part  at 
least  of  the  fibers  must  be  in  relation  with  the  parietal  lobe,  a 
connection  which  Hoche's  case  does  not  take  into  account.  It 
would  seem  that  the  view  of  Mott  must  be  the  more  correct 
one,  since  he  has  shown  that  a  part  of  the  fibers  of  this   tract 


Fig.  ii8. — Course  anu  Tekmi.nation  of  Gowers'  Tract. — {According  to  Hoche.) 

(crossed  afferent  tract  of  Gowers  and  Edinger)  terminates  in 
the  optic  thalamus,  which  we  know  is  in  connection  with  the 
parietal  lobe. 

The  ground  bundles  of  the  lateral  columns  enter  the  formatio 
reticularis  of  each  side,  chiefly  the  lateral  portions.  Many  of 
the  fibers  end  about  the  collections  of  cells  therein  (nucleus 
redcularis  tegmenti).  The  remainder,  according  to  Bechterew, 
continue  brainward  to  the  region  of  the  posterior  corpus  quad- 
rigeminum,  where  the  fibers  end  in  a  special  collection  of  nerve- 
cells  for  each  side  in  the  central  part  of  the  formatio  reticularis, 
named  by  Bechterew  the  superior  central  nucleus.    The  remain- 


THE   REGION   OF    THE   MID-BRAIN.  235 

ing  tracts  of  fibers,  of  short  course,  are  probably  the  axones  of 
the  cells  of  the  formatio  reticularis,  whose  chief  function  is  to 
connect  the  different  levels  of  the  medulla,  pons,  and  brain-stem. 
In  Golgi  specimens  it  will  be  found  that  most  of  the  axones, 
after  a  short  course,  decussate  in  the  raphe,  then  fork,  one 
division  passing  upward,  the  other  downward,  and  they  prob- 
ably arborize  about  cells  of  a  like  character  at  higher  and  lower 
levels.  Some  of  the  axones  do  not  decussate,  but  after  a  short 
course  bifurcate  in  the  same  manner. 


THE  MOTOR  OCULI,  OR  THIRD  PAIR  OF  CRANIAL 

NERVES. 

This  is  the  common  motor  nerve  of  the  eyeball  and  innervates 
all  the  external  muscles  of  the  eye  save  the  superior  oblique 
and  external  rectus.  It  also  supplies  the  sphincter  pupillse  and 
the  ciliary  muscle,  through  its  connection  with  the  ciliary  gan- 
glion. The  origin  of  this  nerve,  on  each  side,  is  from  a  nucleus 
situated  between  the  anterior  corpora  quadrigemina  and  beneath 
the  floor  of  the  ventral  portion  of  the  aqueduct  of  Sylvius,  just 
outside  of  or  lateral  to  the  raphe.  It  extends  ventrally  as  far  as 
the  posterior  portion  of  the  third  ventricle  and  dorsally  to 
beneath  the  middle  of  the  posterior  corpus  quadrigeminum, 
where  it  becomes  continuous  with  the  nucleus  of  origin  of  the 
trochlearis  or  patheticus  nerve,  this  latter  nucleus  being  simply 
the  posterior  continuation  of  the  former.  The  oculomotor 
nucleus  is  composed  of  large  and  small  multipolar  nerve-cells, 
containing  a  yellowish  pigment  and  arranged  on  each  side  into 
an  anterior,  posterior,  and  median  group.  The  anterior  group 
is  located  in  the  wall  of  the  posterior  part  of  the  third  ventricle, 
and  consists  of  a  group  of  small,  multipolar  nerve-cells  whose 
axones  pass  dorsally.  Posterior  to  this  group  exists  the  main 
part  of  this  nucleus,  called  the  posterior  group,  the  axones  of 
the  median  cells  of  which  pass  inward,  decussate  with  their  fellows 
of  the  opposite  side,  and  join  the  opposite  oculomotor  nerve, 
while  the  axones  of  the  other  cells  of  this  group  pass  out  on  the 
same  side  without  decussation.  The  median  cell-group  is  just 
beneath  the  aqueduct  of  Sylvius  and  between  the  main  divisions 


23f 


CENTRAL  NERVOUS  SYSTEM. 


of  the  two  posterior  groups,  aiid  its  axones  pass  on  each  side 
toward  the  oculomotor  nerve-roots  of  that  side.  Just  anterior  to 
the  median  cell  group  exists  on  each  side  two  nuclei,  united  an- 
teriorly and  forming  an  imperfect,  crescent-shaped  mass.  The 
cells  of  this  group  are  small,  and  are  embedded  in  a  dense 
tano-le  of  fibers.  It  is  not  at  present  known  whether  this 
nucleus  on  each  side  is  connected  with  the  nucleus  of  the  oculo- 
motor nerve  or  whether  it  is  independent.  It  was  discovered 
by  Edinger  and  Westphal,  and  receives  the  joint  names  of  both. 


Fig.    119. — MiCROPHOTOGRAPH    THROUGH    THE  NUCLEUS   OF  ORIGIN   OF  THE   MOTOR  OCULI 
Nerve.     Showing  the  multipolar  cells  of  this  nucleus.     Golgi  preparation. 

The  experiments  of  Hensen  and  Voelkers  on  dogs,  and  the 
clinical  observations  of  Pick.  Kahler,  Oppenheim,  Starr,  and 
others,  lend  support  to  the  theory  that  the  oculomotor  nucleus 
consists  of  a  series  of  centers  arranged  from  before  backward, 
which  are  presumably  as  follows,  in  order  from  before  backward  : 
First,  a  group  of  cells  concerned  in  accommodation  ;  second, 
those  presiding  over  the  reflex  action  of  the  iris  to  light ;  then 
cells  for  the  innervation  of  the  followinof  muscles — internal  rec- 
tus,  superior  rectus,  levator  palpebrse  superioris,  inferior  rectus, 


THE   REGION   OF    THE   MID-BRAIN. 


237 


inferior  oblique,  and   superior  oblique,  the  latter  muscle  being 
supplied  by  the  patheticus,  or  fourth  nerve. 

The  axones  from  these  various  cell  groups  pass  ventrally 
through  the  tegmentum,  some  between  and  others  through  the 
mesial  portion  of  the  red  nuclei,  to  reach  the  base  of  the  brain, 


Fig.  120. — A  Camera  Lucida  Drawing  through  the  Nuclei  of  Origin  of  the  Third 
OR  Motor  Oculi  Nerves.  Showing  the  location  of  the  nuclei  and  their  cells,  together 
with  the  descending  axones  from  those  cells  which  go  to  form  the  nerve-roots. 


where  they  emerge  from  a  groove — the  sulcus  oculomotorius — 
as  two  thick,  roundish  nerves,  which  become  located  in  the  inter- 
peduncular space  close  to  the  inner  side  of  each  peduncle  and 
just  above  the  pons  Varolii.  They  then  pass  between  the  supe- 
rior cerebellar  peduncle  and  posterior  cerebral  artery,  forw^ard 
to  the  outer  side  of  the  posterior  clinoid  process,  just  anterior  to 


238 


CENTRAL  NERVOUS  SYSTEM. 


which  they  pierce  the  dura  mater,  forming  the  outer  boundary 
of  the  cavernous  sinus,  and  continuing  forward  they  enter  the 
sphenoid  fissures,  where  each  nerve  divides  into  two  bundles, 
a  superior  and  an  inferior,  which  enter  the  orbit  between  the 
heads  of  the  external  rectus  muscle.  The  superior  bundle 
passes  over  the  optic  nerve  to  supply  the  superior  rectus  and 
levator  palpebrre  superioris  muscles.  The  inferior  bundle 
divides  into  three  parts — one  for  the  internal  rectus,  one  for  the 
inferior    rectus,    and    the    third,    the    longest,    for   the   superior 


Nuei.ESINGEIt- 


NUCU  l.»T.  ANT\        \ 
(OARKSCMCWITSCHJ 


Fig.  121. — Diagram  of  the  Groups  of  Cells  Forminc;  the  Nuclei  of  the  Third  and 
Fourth  Cranial  Nerves. — {AfUr  Perliafrom  Quain.) 

oblique.  This  latter  branch  is  also  connected  with  the  ciliary 
ganglion,  and  contains  fibers  for  the  ciliary  muscle  and  sphincter 
of  the  pupil. 


THE  CONNECTIONS  OF  THE  OCULOMOTOR  NUCLEUS. 

First,  with  the  motor  or  pyramidal  tract,  by  collaterals  which, 
after  decussating,  arborize  about  the  cells  of  the  nucleus  of  the 
third  nerve  of  the  opposite  side  ;  second,  with  the  posterior  longi- 
tudinal bundle.     This  bundle  is  chiefly  connected  with  the  oculo- 


THE   REGION   OF    THE   MID-BRAIN. 


239 


motor  nucleus  of  the  opposite  side,  although  a  few  fibers  pass 
to  the  nucleus  of  the  same  side.  We  may  here  recall  the  fact 
that  the  posterior  longitudinal  bundle  is  also  connected  with  the 
nuclei  of  the  fourth  and  sixth  nerves.  Owing  to  the  latter  con- 
nection, the  conjugate  or  associative  movements  of  the  eyeballs 
may  take  place  ;  thus,  if  both  eyes  are  turned  to  the  right,  the 
right  eye  turns  to  the  right  by  virtue  of  a  contraction  of  the  right 
external  muscle,  innervated  by  the  right  abducens  or  sixth  nerve^ 
while  the  left  eye  deviates  to  the  right  owing  to  a  contraction  of 


D.P.N. 


p.L.a. 


Fig.  122. — Transverse  Section  Through  the  Mid-brain  at  the  Level  of  the 
Posterior  Corpora  Quadrigemina.     Weigert  preparation. 
D.P.N.    Decussation  of  the  patheticus  or  fourth  pair  of  cranial  nerves.      P.C.N.   Posterior  cor- 
pora quadrigemina.      P.L.B.    Posterior  longitudinal  bundle,  showing  its  relation  to  the  root 
fibers  of  the  third  nerve. 


the  left  internal  rectus,  innervated  by  the  left  motor  oculi  nerve  ; 
hence,  both  eyes  are  moved  conjointly  to  the  right  by  the  activity 
of  the  two  chief  motor  nerves  of  the  eye,  associated  through  the 
posterior  longitudinal  bundle.  The  third  connection  is  with  the 
optic  tract,  possibly  through  cells  in  the  anterior  corpus  quadri- 
geminum,  whose  axones  and  collaterals  arborize  about  the  cells 
of  this  nucleus  (Koelliker).  According  to  Darschewitsch,  how- 
ever, this  connection  is  made  by  a  small  bundle  of  fibers  leaving 
the  mesial  portion  of  the  optic  tract  to  pierce  the  optic  thalamus 


240  CENTRAL  NKRVOUS  SVSTLM. 

and  to  reach  the  oculomotor  nucleus  throiuj^h  the  posterior  com- 
missure. This  connection  completes  the  reflex  arc,  by  means 
of  which  the  pupillary  reflexes  are  subserved. 


THE  FOURTH  PAIR  OF  CRANIAL  NERVES. 
This  pair,  called  on  each  side  the  patheticus,  or  trochlearis. 
arises  from  a  collection  of  medium-sized  (40  to  50  u)  multi- 
polar nerve-cells  located  beneath  the  anterior  part  of  the  infe- 
rior or  posterior  corpus  quadrigeminum.  in  the  ventral  gray 
matter  of  the  aqueduct  of  Sylvius,  and  internal  to  the  descend- 
ing root  of  the  fifth  nerve.  This  group  of  cells  is  continuous 
anteriorly  with  the  oculomotor  nucleus,  and  is  in  reality  the 
dorsal  continuation  of  that  nucleus.  The  axones  from  the  cells 
of  this  nucleus  pass  downward  toward  the  pons  Varolii,  then 
curve  dorsally  around  the  lower  part  of  the  Sylvian  aqueduct  to 
enter  the  superior  medullary  velum,  there  to  completely  decus- 
sate with  their  fellows  of  the  opposite  side.  The  two  nerves 
emerge  just  below  the  inferior  quadrigeminal  bodies,  and,  pass- 
ing downward  across  the  superior  peduncles  of  the  cerebellum, 
wind  around  the  outer  side  of  each  crus  cerebri,  where  they  are 
to  be  seen.  Each  nerve  then  pierces  the  dura  mater  behind  the 
posterior  clinoid  process,  and  runs  forward  in  the  wall  of  the 
cavernous  sinus  lying  against  the  ophthalmic  nerve,  and  then, 
crossing  the  third  nerve  obliquely,  enters  the  sphenoid  fissure 
and  ramifies  on  the  superior  oblique  muscle  (Figs.  121  and  122). 


THE    SUPERIOR    OR    ACCESSORY     NUCLEUS    OF    THE 
FIFTH  OR  TRIGEMINAL  NERVE. 

This  nucleus  ■■='  consists  of  a  collection  of  multipolar  cells 
slightly  crescent-shaped,  located  in  the  central  gray  matter,  at 
the  lateral  border  of  the  aqueduct  of  Sylvius,  and  beneath  the 
posterior  corpus  quadrigeminum.  A  few  cells  of  this  nucleus 
frequently  extend  forward  as  far  as  the  beginning  of  the  ante- 

*The  cells  of  the  superior  or  accessory  trigeminal  nucleus  are  believed  to  be  multipolar  by 
Koelliker  and  Obersteiner,  while  Ram6n  y  Cajal,  I.ugaro,  and  Golgi  think  they  are  without 
dendrites,  and  are  pear-shaped,  unipolar  cells. 


Ga. 


SSCfi 


Fig.  123.— Schematic,  Representation  of  the  Origin  of  the  Trigeminal  Nerve.— 

[After  E dinger.) 
^6  "  241 


THE   REGION   OF    THE   MID-BRAIN.  243 

rior  corpus  quadrigeminum.  The  nucleus  probably  extends 
caudad  to  the  anterior  extremity  of  the  fourth  ventricle,  where  it 
is  continuous  on  each  side  with  the  darkly  pigmented  cells  of 
the  substantia  ferruginea,  which  are  grouped  on  each  side  of 
the  ventricle,  lateral  to  the  posterior  longitudinal  bundles  and 
beneath  the  ependyma,  and  are  covered  by  a  bluish-gray  area, 
— the  locus  coeruleus, — through  which  this  dark  group  of  cells 
may  be  seen.  This  group  may  be  considered  as  part  of  the 
nucleus,  since  Mendel  found  them  wasted  in  a  case  of  progres- 
sive facial  atrophy  where  the  fibers  of  the  trigeminal  nerve  of 
that  side  were  degenerated.  The  axones  from  the  cells  of  the 
accessory  trigeminal  nucleus  join  the  portiominor  or  motor  divi- 
sion of  the  fifth  nerve  ;  they  are  probably  motor  in  function, 
although  Merkel  believes  they  may  have  a  trophic  function, 
while  Huguenin  thinks  they  have  a  vasomotor  function. 


chaptp:r  VI. 
REGION  OF  THE  THIRD  VENTRICLE. 

From  the  primary  cerebral  vesicle  is  developed  the  'tween 
brain,  called  also  interbrain,  or  thalamencephalon  ;  this  includes 
the  third  ventricle,  pineal  bocly  or  gland,  optic  thalami,  optic 
tracts,  infundibulifm  and  pituitary  body,  middle  and  posterior 
commissures,  posterior  perforated  spaces,  corpora  albicantia  or 
mammillaria,  tuber  cinereum,  and  lamina  cinerea.  This  region 
is  between  the  secondary  fore-brain  (cerebral  hemispheres  and 
contained  ganglia)  anteriorly  and  superiorly  and  the  mid-brain, 
consisting  of  the  corpora  quadrigemina  and  crura  cerebri,  pos- 
teriorly and  inferiorly.  It  is  connected  anterolaterally  with  the 
cerebral  hemispheres,  and  they  rest  upon  its  superior  surface 
with  only  pia  mater  intervening.  Posteriorly  it  is  connected  with 
the  corpora  quadrigemina. 


THE    THIRD  VENTRICLE. 

This  ventricle  is  the  remains  of  the  primary  cerebral  vesicle. 

It  is  a  deep  but  narrow  cavity,  placed  between  the  optic  thalami 

and  extending  to   the  base  of  the  brain.     Above   it  exists  the 

fornix  and  corpus  callosum.     It  has  for  its  roof  the  velum  inter- 

positum  lined  with  epithelium,  from  which  are  suspended  the 

choroid  plexuses    for  this  ventricle.     Its    floor  is  composed  of 

the  parts  which  exist  in  the  interpeduncular  space,  which  are, 

from   before  backward,  the  lamina  cinerea,  tuber  cinereum,  in- 

fundibulum,    corpora    albicantia,    posterior     perforated     space, 

and  part  of  the  tegmentum.     Its  lateral  boundary  is,  in  reality, 

the    surrounding    central    gray    matter,     although    anatomists 

generally  state  that  this   boundary  is   the  optic  thalamus.     The 

optic    thalami    lie    very    close    to   each    other  just   anterior    to 

244 


REGION   OF    THE   THIRD   VENTRICLE. 


245 


the  middle  part  of  the  ventricle,  and  are  connected  by  a  trans- 
verse bundle  of  fibers — the  middle  or  soft  commissure.  This 
commissure  is  the  result  of  the  union  of  the  mesial  surfaces  of 
the  thalami,  which  occurs  at  about  the  fifth  month  of  fetal  life. 


P-O.T. 


Fig.  124. — Horizontal  Section  through  the  Ckrebral  Hemispheres  to  Show  the 
Region  of  the  Third  Ventricle. 

A.M.F.  Anterior  median  fissure.  A.H.  Anterior  horn  of  lateral  ventricle.  A  P.F.  Anterior 
pillar  of  fornix.  H.C.N.  Head  of  caudate  nucleus.  A.C.  Anterior  commissure.  M.C. 
Middle  or  soft  commissure.  3rd.V.  Third  ventricle.  O.T.  Optic  thalamus.  P.  P.G. 
Peduncle  of  pineal  gland.  T.C.N.  Tail  of  caudate  nucleus.  P.G.  Pineal  gland. 
A.C.Q.  Anterior  corpora  quadrigemina.  P.C.Q.  Posterior  corpora  quadrigemina.  C.P.L.V. 
Choroid  plexus  of  lateral  ventricle.  F.  Fornix.  C.P.3rd.V.  Choroid  plexus  of  third  ven- 
tricle. P.H.  Posterior  horn.  D.H.  Descending  horn.  P. O.T.  Pulvinar  of  optic  thala- 
mus.    P.C.   Posterior  commissure.     V.C.S.  Vena  corpora  striati.     C.C.   Corpus  callosum. 

It  is  frequently  absent,  and  is  so  soft  that,  unless  great  care  be 
used  in  removing  or  manipulating  the  brain,  it  will  be  torn. 

The  anterior  part  of  the  floor  of  the  ventricle  is  separated  from 
its  lateral  walls  by  the  prominent  anterior  pillars  or  columns  of  the 
fornix,  which  are  lined  at  this  point  by  the  central  gray  matter  of 


240  CENTRAL  NERVOUS  SYSTEM. 

the  ventricle,  lust  anterior  to  the  fornix  passes  the  anterior  com- 
missure ;  between  the  anterior  pillars  of  the  fornix  and  the  ven- 
tral part  of  each  optic  thalamus  exists  an  aperture  which  leads 
into  the  lateral  ventricle  on  each  side.  This  is  the  foramen  of 
Monro,  which  is  the  only  means  of  connection  between  the  third 
and  lateral  ventricles.  The  peduncles  of  the  pineal  gland  run 
along  on  each  side  of  the  superior  part  of  the  margin  of  the 
la.teral  walls  of  the  ventricle.  This  cavity  is  limited  posteriorly 
by  the  entrance  or  opening  of  the  aqueduct  of  Sylvius,  by  the 
posterior  commissure,  and  by  a  reflection  of  epithelium  from  the 
upper  surface  of  the  pineal  gland  upon  the  under  surface  of  the 
velum  interpositum.  The  cavity  of  the  ventricle  is  more  shallow 
behind  than  in  front.  The  deep  anterior  portion  of  it  passes  to 
a  conic  termination,  which  lies  above  the  optic  commissure, 
called  the  optic  recess ;  behind  this  recess  is  another  depression, 
the  infundibulum,  which  leads  to  the  pituitary  body  or  hypoph- 
ysis cerebri.  At  the  posterior  extremity  of  the  cavity,  above 
the  entrance  of  the  Sylvian  aqueduct,  is  a  depression  which 
extends  backward  to  the  stalk  of  the  pineal  gland,  or  conarium. 
The  third  ventricle  has  four  openings — viz.,  those  of  the  foramen 
of  Monro,  one  on  each  side,  communicating  with  the  lateral 
ventricles,  the  opening  of  the  aqueduct  of  Sylvius,  which  com- 
municates with  the  fourth  ventricle,  and  that  of  the  infundibulum. 
This  cavity  is  lined  with  ciliated  epithelium,  which  fills  in  all  its 
inequalities,  is  reflected  over  the  mesial  surfaces  of  the  optic 
thalami  and  upon  the  velum  interpositum  and  choroid  plexuses. 
The  epithelium  rests  upon  a  thin  layer  of  ependymal  tissue,  be- 
neath which  is  the  central  gray  matter,  which  is  continuous  with 
that  lining  the  aqueduct  of  Sylvius — a  prolongation  of  the  gray 
matter  of  the  fourth  ventricle.  It  extends  upon  the  mesial 
surfaces  of  the  optic  thalami  and  rests  posteriorly  upon  the 
tegmentum.  In  front  and  below,  it  comes  to  the  surface  as  the 
posterior  perforated  space  and  tuber  cinereum. 


THE  PINEAL  GLAND,  OR  CONARIUM. 
The  pineal  gland,  also  termed  epiphysis  cerebri,  receives  its 
name  because  of  its  supposed   resemblance  to  a  fir-cone,  the 


REGION   OF    THE   THIRD   VENTRICLE.  247 

Latin  to-rm.  pimcs  being  the  generic  name  for  a  class  of  the  cone- 
bearing  trees.  It  is  a  small,  reddish-gray  body  about  the  size 
of  a  bean,  but  conic  in  form.  It  is  dorsal  to  the  posterior 
commissure,  with  which  it  is  connected,  and  lies  a  little  ventral 
to  and  between  the  superior  or  anterior  corpora  quadrigemina. 
It  is  retained  in  place  by  a  duplicature  of  pia  mater  from  the 
under  surface  of  the  velum  interpositum.  It  is,  according  to 
Schwalbe,  twelve  millimeters  in  its  anteroposterior,  eight  in  its 
transverse,  and  four  in  its  vertical  diameter.  It  is  connected 
with  the  rest  of  the  cerebrum  by  a  broad,  flat  bundle  of  white 
fibers,  which  bundle  is  separated  by  the  pineal  recess  into  a 
dorsal,  or  superior,  and  ventral,  or  inferior,  lamina.  The  upper 
or  dorsal  lamina  (pedunculus  conarii)  sends  a  bundle  of  fibers 
to  the  right  and  left  into  each  optic  thalamus.  This  lamina  is 
also  continuous  on  each  side  with  the  trigonum  habenulse,  and 
its  anterior  portion  continues  forward  as  the  peduncle  of  the 
pineal  gland,  along  the  margin  of  the  third  ventricle,  and  passes 
into  the  ganglion  habenulse.  The  lower  or  ventral  lamina 
passes  into  the  posterior  commissure.  These  fibers  are  derived 
probably  from  the  optic  tract,  and  pass  into  the  opposite  oculo- 
motor nucleus.  The  pineal  gland  is  covered  by  pia  mater, 
which  sends  into  its  interior  a  number  of  vascular  connective- 
tissue  processes,  which  divide  the  gland  into  a  number  of 
spheric  or  tubular  spaces  called  follicles,  which  latter  are  Hned 
with  epithelium  similar  to  that  of  the  lymph-glands.  These 
follicles  are  filled  with  calcareous  granules  composed  of  the 
phosphates  and  carbonates  of  the  alkaline  earths,  which  gran- 
ules bear  the  name  of  the  acervulus  cerebri,  or  brain-sand. 
The  gland  is  a  hollow  outgrowth  of  the  medullary  wall  of  the 
roof  of  the  primary  fore-brain  vesicle,  which  latter  afterward 
forms  the  third  ventricle.  The  gland  becomes  separated  from  the 
ventricular  cavity,  after  which  numerous  small  processes  bud  out 
from  its  inner  walls  and  coalesce,  forming  its  crypts.  Cajal 
has  shown  that  n6rve-fibers  and  cells  are  found  in  this  gland. 
These  nerve-fibers  belong  to  the  sympathetic  system,  and  ac- 
company the  large  vessels  into  the  gland  ;  they  then  leave  the 
vessels,  pass  between  the  follicles,  and  repeatedly  branch  and 
unite  with  each  other,  forming  an  interstitial  plexus;  they  end 


248  CENTRAL  NERVOUS  SYSTEM. 

free  in  varicose-like  arborizations  or  club-shaped  thickenings. 
The  nerve-cells  lie  between  the  follicles  ;  they  are  small  sphe- 
roid or  irregular-shaped  cells,  with  two  to  four  dendrites,  which 
vary  as  to  length,  some  being  rather  short,  while  others  are 
moderately  long.  They  terminate  with  thickened  free  extremi- 
ties. 

THE  POSTERIOR  COMMISSURE. 
This  is  a  fasciculus  of  medullated  fibers,  mostly  transverse, 
which  overlies  the  entrance  of  the  aqueduct  of  Sylvius  into  the 
third  ventricle.  It  is  located  in  the  posterior  wall  of  the  latter 
cavity.  The  pineal  gland  is  just  above  and  slightly  dorsal  to 
it.  A  part  of  the  fibers  of  the  ventral  portion  of  this  commis- 
sure originate  in  the  ganglia  subthalami,  deep  in  the  inter- 
brain  on  each  side  of  the  raphe.  These  fibers  proceed  dorsally 
to  reach  the  region  just  back  of  the  corpora  quadrigemina,  where 
they  decussate  with  their  fellows  of  the  opposite  side  and 
pass  into  the  tegmental  region  of  that  side,  close  to  the  poste- 
rior longitudinal  bundle,  possibly  being  associated  with  that 
bundle.  They  then  continue  downward  to  the  medulla.  Dark- 
schewitch  asserts  that  the  )rliedian  fibers  of  this  bundle  pass  into 
the  nucleus  of  the  oculomotor  nerve,  and  that  the  dorsal  bundle 
of  the  commissure  passes  into  the  corona  radiata  of  the  hemi- 
sphere connecting  it  with  the  opposite  superior  corpus  quadri- 
geminum.  According  to  Meynert,  most  of  the  fibers  of  this 
commissure  are  continuations  of  the  fibers  of  the  fillet,  which, 
after  decussating,  pass  through  the  optic  thalamus  into  the 
corona  radiata  of  the  opposite  side. 


THE  OPTIC  THALAMI. 

These  are  two  large,  oblong  masses,  chiefly  of  gray  matter, 
appearing  to  be  w^edged  in  between  the  corpora  striata  and  to 
rest  upon  the  crura  cerebri.  Their  superior  or  dorsal  surfaces 
are  covered  by  a  thin  mantle  of  white  fibers — the  stratum 
zonale.  They  are  developed  from  the  lateral  walls  of  the  inter- 
brain.  On  the  outer  side  of  each  thalamus  is  the  posterior  limb 
of  the  internal  capsule.     Their  internal  surfaces  form,  with  the 


REGION   OF    THE   THIRD   VENTRICLE.  249 

central  gray  matter,  the  outer  boundaries  or  walls  of  the  third 
ventricle.  A  small  part  of  each  thalamus  assists  in  forming  the 
floor  of  the  lateral  ventricle.  Above  exists  the  fornix,  separated 
from  the  optic  thalamus  by  the  velum  interpositum.  Each  optic 
thalamus  has  four  distinct  surfaces — superior  or  dorsal,  inferior 
or  ventral,  internal  or  mesial,  and  external  or  lateral.  The 
superior  surface  is  separated  from  the  nucleus  caudatus  by  a 
groove,  which  contains  the  vena  corpora  striata  and  a  fasciculus 
of  fibers — the  taenia  cornea  or  semicircularis,  or  the  stria 
terminalis.  This  surface  is  divided  by  a  slight  longitud- 
inal depression  corresponding  to  the  thickness  of  the  fornix, 
which  lies  above  it,  called  the  sulcus  choroideus,  dividing  it 
into  a  mesial  and  a  lateral  portion.  The  lateral  portion  of  this 
depression  is  found  in  the  floor  of  the  body  of  the  lateral  ven- 
tricle, and  is  covered  with  epithelium  common  to  the  lateral 
ventricle.  Anteriorly  this  portion  grows  into  a  distinct  promi- 
nence, called  the  anterior  tubercle.  The  surface  internal  or 
mesial  to  the  sulcus  is  covered  by  the  velum  interpositum.  It 
is  separated  from  the  inner  or  mesial  surface  by  the  peduncles 
of  the  pineal  gland.  At  the  posterior  and  inner  part  of  this 
area  exists  a  large  and  important  prominence — the  pulvinar. 
It  overlaps  the  brachia  of  the  corpora  quadrigemina.  Between 
the  pulvinar  and  the  beginning  of  the  peduncle  of  the  pineal 
gland  on  each  side  exists  a  depressed  area  of  gray  matter, 
called  the  trigonum  habenulcE.  Ventral  to  the  trigonum  exists 
a  small,  club-shaped  swelling — the  ganglion  habenula. 

The  internal  or  mesial  surface  of  each  thalamus  is  almost  fiat, 
and  forms  the  outer  boundary  of  the  third  ventricle.  It  is  cov- 
ered by  the  ventricular  epithelium,  which  rests  upon  a  very  thin 
layer  of  ependyma,  which  gives  to  the  surface  a  pale-gray  color. 
It  is  united  with  its  fellow  of  the  opposite  side  by  the  middle  or  soft 
commissure.  The  external  and  lateral  surface  forms  the  inner 
boundary  of  the  posterior  limb  of  the  internal  capsule.  This  limb 
of  the  capsule  separates  the  thalamus  from  the  lenticular  nucleus. 
This  area  extends  from  the  anterior  extremity  of  the  thalamus 
backward  to  the  pulvinar,  and  is  called  the  lateral  nucleus.  Both 
extremities  are  somewhat  rounded ;  the  posterior  extremity  is 
composed  almost  entirely  of  the  prominence  called  the  pulvinar, 


250 


CENTRAL  NERVOUS  SYSTEM. 


which  latter  is  made  up  principally  of  gray  matter — and  is  con- 
nected both  with  the  optic  tract  and  occipital  lobe ;  on  the  posterior 
and  inferior  surfaces  of  the  pulvinar  exist  two  elevations  of  gray 
matter — the  internal  and  external  creniculate  bodies.  The  in- 
ternal  geniculate  body  is  an  oval  elevation,  located  on  the  inferior 
and  inner  side  of  the  pulvinar  between  the  brachia  of  the  corpora 
quadrigemina.      Below  and  external  to  it.  and  continuous  ante- 


FiG.  125. — Section  through  the  Superior  Part  of  One  of  the  Superior  Corpora 
Quadrigemina  and  the  Adjacent  Part  of  the  Optic  Thalamus. — {After  Mey- 
neri.) — {From  Quain' s  '^Anatomy.") 

s.  Aqueduct  of  Sylvius,  gr.  Gray  matter  of  the  aqueduct,  c.t/.s.  Quadrigeminal  eminence, 
consisting  of:  /.  Stratum  lemnisci.  0.  Stratum  opticum.  c.  Stratum  cinereum.  77/. 
Thalamus  (pulvinar).  c.g.i,  c.g.e.  Internal  and  external  geniculate  1  odies.  br.s,  br.i. 
Superior  and  inferior  brachia.  /  Upper  fillet.  /./.  Posterior  longitudinal  bundle,  r. 
Raphe.  ///.  Third  nerve ;  n.III;  its  nucleus.  /././.  Posterior  perforated  space,  s.n. 
Substantia  nigra.  Above  this  is  the  tegmentum  with  its  nucleus,  the  latter  being  indicated 
by  the  circular  area.  cr.  Crusta.  //.  Optic  tract.  M.  Medullary  center  of  the  hemi- 
sphere,    ti.c.  nucleus  caudatus.     st.   Stria  terminalis. 


riorly  with  the  optic  tract,  is  a  small,  club-shaped  body,  about  the 
size  of  a  bean,  called  the  external  or  lateral  geniculate  body. 

The  internal  geniculate  body  is  covered  with  a  layer  of  white 
fibers,  and  contains  a  number  of  small,  multipolar  nerve-cells, 
each  from  20  to  25  ii  in  diameter,  and  is  connected  on  each  side 
with  the  auditory  tract. 

The  external  or  lateral  geniculate  body  is  of  a  yellowish-gray 


REGION   OF    THE   THIRD   VENTRICLE. 


251 


color, — owing  to  the  preponderance  of  gray  matter, — contains 
multipolar  nerve-cells  of  from  30  to  40  ^  in  diameter,  possessing 
many  dendrites  radiating  from  all  parts  of  the  cell-body.  This 
body  receives  fibers  from  the  optic  tract,  axones  from  the  multi- 
polar cells  of  the  retina. 

Both  these  bodies  are  connected  with  the  corpora  quadrigem- 
ina,  the  internal  being  connected  with  the  posterior  or  inferior 


B 

Fig.  126. — Frontal  Section  through  Basal  Ganglia  to  show  the  Nuclei  of  the 
Optic  Thalamus. — {After  von  Monakow.') — [From  Starr's  "  Atlas.'') 

B.  Section  at  junction  of  middle  and  anterior  two-thirds  of  the  thalamus.  OT.  Optic  thalamus. 
lat.  Lateral  nucleus.  nied.  Median  nucleus.  vent.  Ventral  nucleus.  ta.  Anterior 
nucleus.         Int.  Cap.   Internal  capsule.     LN.   Lenticular  nucleus.     /:  Lenticular  loop. 

corpus  quadrigeminum  and  the  external  with  the  anterior   or 
superior  corpus  quadrigeminum. 

The  optic  thalami  have  a  double  connection  with  all  parts  of 
the  cerebral  cortex  :  first,  by  bundles  of  fibers  from  the  different 
nuclei  of  the  thalami  (von  Monakow),  called  the  projection  fibers 
of  these  bodies  ;  and,  secondly,  by  axones  from  the  pyramidal 
cells  of  all  parts  of  the  cortex.  .  In  a  general  way,  according  to 
von  Monakow,  the  thalami  are  anatomically  related  with  the  cere- 


252 


CENTRAL  NERVOUS  SYSTEM. 


bral  cortex,  as  follows  :  The  anterior  and  mesial  portions  of  the 
thalamiare  in  relation  with  the  frontal  lobes  ;  the  lateral  area  or 
ganglion  with  the  parietal  lobe ;  the  ventral  ganglion  with  the 
operculum  ;  the  posterior  ganglion,  corpus  geniculatum  exter- 
num, and  pulvinar  with  the  gyri  of  the  occipital  lobe;  the  corpus 
geniculatum  internum  and  posterior  ganglion  with  the  temporal 
lobe.  This  projection  system  of  fibers  passes  through  the  in- 
ternal capsule  in  bundles,  which  have  been  termed  laminae 
medullares,  or  peduncles  of  the  optic  thalamus.     They  divide 


Fig.    127. — MiCROPHOTOGRAPH    THROUGH    QPTIC    THALAMUS    SHOWING    BUSCH    CELLS. 

Golgi  method. 


each  thalamus,  accordino-  to  von  Monakow,  into  the  followincr  nu- 
clei :  the  anterior  or  tuberculum  anterius,  the  median,  the  lateral, 
the  ventral,  the  posterior,  and  the  pulvinar.  The  geniculate 
bodies  and  the  ganglion  habenulae  are  so  closely  associated  with 
the  optic  thalamus  that  they  will  be  described  with  that  body. 

The  anterior  nucleus,  or  tuberculum  anterius,  is  the  promi- 
nence on  the  anterior  portion  of  the  dorsal  surface  of  the 
thalamus,  lateral  to  its  sulcus  choroideus.  It  is  surrounded  on 
all  sides  by  the  white  substance,  and  its  free  surface  is  covered 


REGION   OF    THE   THIRD   VENTRICLE.  253 

by  the  fibers  called  the  stratum  zonale.  Some  axones  from  the 
cells  of  this  nucleus  pass  downward  to  the  base  of  the  brain, 
ending  in  the  corpus  albicans  or  mammillare,  forming  the 
bundle  of  Vicq  d'Azyr  or  fasciculus  thalamomammillaris,  thus 
establishing  a  connection  between  the  optic  thalamus,  the  gyrus 
hippocampus,  uncinate  gyrus,  and  cornu  ammonis.  The  cells 
of  this  latter  region  give  origin  to  the  fornix  fibers,  which  end  in 
the  corpus  mammillare.  Von  Monakow  found  in  several  cases 
where  these  regions  were  diseased  an  atrophy  of  the  fimbria,  of 
the  anterior  pillar  of  the  fornix,  and  of  the  corpus  mammillare  of 
the  same  side. 

The  median  nucleus  is  posterior  and  inferior  to  the  anterior 
nucleus.  It  has  been  divided  by  von  Monakow  into  a  median  and 
a  lateral  portion.  It  extends  backward  to  the  trigonum  habenulae. 
External  to  it  is  the  lateral  nucleus,  while  below  and  adjacent  is 
the  ventral  nucleus.  It  is  connected  with  the  island  of  Reil  and 
the  second  and  third  frontal  gyri.  The  lateral  nucleus  occupies 
the  entire  lateral  surface  of  the  thalamus,  resting  against  the 
internal  capsule.  It  is  the  largest  of  the  nuclei,  and  extends 
from  the  anterior  extremity  of  the  thalamus  posteriorly  to  the 
pulvinar.  It  receives  from  the  cerebral  cortex  numerous  fibers, 
which  come  from  the  reo:ion  of  the  central  convolutions. 

The  ventral  nucleus  is  located  beneath  the  median  and  lateral 
nuclei,  and  occupies  the  entire  ventral  surface  of  the  thalamus. 
It  lies  close  to  the  lower  portion  of  the  internal  capsule.  Accord- 
ing to  von  Monakow,  the  anterior  portion  of  this  nucleus  is  in 
relation  anatomically  with  the  frontal  lobe,  the  remainder  being 
in  relation  with  the  parts  of  the  cerebral  cortex  about  the  fissure 
of  Sylvius — viz.,  the  operculum,  central  gyri,  and  the  supra- 
marginal  gyrus. 

The  posterior  nucleus  is  located  beneath  the  pulvinar  and 
between  the  geniculate  bodies  ;  it  is  in  anatomic  relation 
with  that  part  of  the  cortex  located  between  the  occipital  and 
temporal  lobes. 

The  pulvinar,  which  occupies  the  posterior  portion  of  the 
optic  thalamus,  has  been  described  on  page  249.  It  is  in  relation 
with  the  9ptic  tract  and  occipital  lobe. 

The  nuclei  of  the  optic  thalamus  contain  three  disdnct  forms 


254  CENTRAL  NERVOUS  SYSTEM. 

of  nerve-cells:  first,  stellate,  or  "  Strahlenzellen  ";  second,  the 
cells  with  brush-like  processes  ("  Buschzellen  "  of  Koellikcr) ; 
third,  the  polygonal  cells,  first  described  by  Starr. 

The  first  variety  exists  throughout  the  optic  thalamus,  but  is 
principally  found  in  the  lateral  and  median  nuclei.  They  have 
been  called  by  Starr  stellate,  and  are  identical  with  the  cells 
described  by  Koelliker  as  the  Strahlenzellen.  They  are  spindle, 
spheric,  or  triangular  in  shape,  35  to  50  u  in  diameter,  and 
give  off  from  four  to  ten  dendrites,  which,  with  their  many 
branching  processes,  radiate  in  all  directions  from  the  cell-body 
— hence  their  name.  A  few  of  the  dendrites  are  very  long,  but 
the  majority  are  short.  They  seldom  possess  granules,  and 
their  branches  do  not  form  brushes  of  fibers.  The  axone  comes 
off  from  the  cell-body  and  gives  off  a  few  collaterals.  Its  course 
can  be  traced  a  short  distance  only.  It  is  probable,  however,  as 
suggested  by  Starr,  that  many  of  the  axones  from  these  cells 
pass  into  the  internal  capsule. 

The  Buschzellen,  or  the  cells  whose  dendritic  processes  are 
arranged  in  brush-like  expansions,  were  discovered  by  Koel- 
liker. They  are  round,  spindle,  or  triangular-shaped  cells,  from 
25  to  40  a  in  diameter,  with  six  to  eight  dendrites,  each  of 
which  repeatedly  divides  into  a  brush  of  very  fine  fibrils. 
Koelliker  has  shown  that  in  preparations  after  the  Golgi  method 
the  main  stem  of  each  dendrite  is  granular,  and  stains  deep 
black,  while  the  brush  of  fine  fibrils  takes  the  stain  less  readily, 
and  is  lighter  in  color.  The  axones  of  these  cells  resemble 
those  of  the  first  variety.  These  cells  are  located  in  the  dorsal 
half  of  the  optic  thalamus,  also  in  the  corpus  geniculatum  lateralis 
of  each  side  and  in  the  gray  matter  about  the  third  ventricle. 

The  polygonal  cells  occur  only — according  to  Starr,  who  dis- 
covered them — in  the  ventral  or  anterior  nucleus  of  the  thalamus. 
They  are  large  cells,  from  50  to  60  u  in  diameter,  polygonal  in 
shape,  and  give  off  from  the  cell-body  a  number  of  very  long, 
slender  dendrites  studded  with  gemmules.  The  course  of  the 
dendrites  is  tortuous,  but  they  do  not  possess  as  many  branches 
as  do  those  from  the  stellate  cells.  The  axone  comes  from  the 
body  of  the  cell,  gives  off  a  few  collaterals,  and,  according  to 
Starr,  has  no  uniform  direction. 


Fig.   128. — MiCROPHOTOGRAPH   THROUGH    OpTIC    THALAMUS    SHOWING   SXELT.ATE   CELLS. 

Method  of  Golgi. 


Fig.    129. — MiCROPHOTOGRAPH    THROUGH   OpTIC   THALAMUS    WITH    A    SINGLE   LARGE 

Polygonal  Cell.     Method  of  Berkley. 


255 


REGION   OF    THE   THIRD   VENTRICLE. 


257 


THE  GANGLION  HABENUL^. 

This  is  a  small  swelling  on  the  anterior  portion  of  the  mesial 
surface  of  the  optic  thalamus.  It  is  united  with  its  fellow  of  the 
opposite  side  by  a  commissural  band — the  dorsal  thalamic  com- 
missure. From  the  cells  of  this  ganglion  a  few  fibers  pass 
backward  to  the  pineal  gland  (Starr).     It  receives  fibers  from 


Fig.  130. — A  Perpendicular  Section  through  the  Brain  of  a  Rabbit  Lateral  to 
THE  Corpus  Mammillare. — [After  Koelliker.) 

CA.  Cornu  ammonis.  Cf.  Columna  fornicis.  Cp.  Commissura  posterior.  Cqa,  Cqp.  Corpora 
quadrigemina.  D  Brc.  Decussation  of  the  superior  cerebellar  peduncles.  Fl.  Fornix. 
FM.  Fasciculus  retroflexus  (Meynert).  Ft.  Fasciculus  tegmenti.  Fihtii.  Fasciculus 
thalamoraammillaris  (Vicq  d'Azyr).  Gb.  Basal  ganglion.  Gh.  Ganglion  habenulas. 
Gl.  Lateral  ganglion  of  corpus  mammillare.  Lni.  Median  lemniscus  or  fillet.  Lo.  Lobus 
olfactorius.  O.  Optic  tract.  P.  Pons.  Pan.  Pedunculis  corporis  mammillaris.  Ps. 
Psalterium.  Sp.  Septum  pellucidum.  St  K.  Head  of  caudate  nucleus.  Strm.  Stria 
merlullaris.  Strm'^.  Connection  of  the  same  with  the  columna  fornicis.  Vni  a.  Anterior 
medullary  velum.  Viv.  Fourth  ventricle.  ///.  Oculomotor  nerve-roots.  X.  Radiation 
of  the  fibers  of  the  peduncle  of  the  corpus  mammillare. 

the  peduncles  of  that  gland.  The  cells  of  this  ganglion  give 
off  axones  which  form  a  bundle  of  fibers — the  fasciculus  retro- 
flexus, or  Meynert's  bundle.*  This  fasciculus  of  fibers  passes 
downward  through  the  tegmentum,  between  the  red  nucleus  and 
posterior  longitudinal  bundle,  giving  off,  according  to  Meynert, 


*  After  destruction  of  the  ganglion  habenulse,  the  fasciculus  retroflexus  of  Meynert  degenerates 
to  its  termination  in  the  interpeduncular  ganglion. 
17 


25S  CENTRAL  NERVOUS  SYSTEM. 

a  few  fibers  to  that  nucleus  ;  then  the  main  bundle  bends  nearly  at 
a  right  angle,  and  proceeds  downward  into  the  tegmentum  of  the 
pons  and  medulla.'''  According  to  Forel,  Gudden,  and  Edinger, 
however,  this  bundle  of  fibers  curves  through  the  tegmentum, 
between  the  red  nucleus  and  posterior  longitudinal  bundle,  and 
ends,  after  decussating  with  its  fellow,  among  a  collection  of 
nerve-cells  existing  in  the  back  part  of  the  posterior  perforated 
space  between  the  crura  cerebri,  called  the  interpeduncular 
ganglion  (Fig.  130). 


CONNECTIONS  OF  THE  OPTIC  THALAMUS. 

First,  each  thalamus  has  a  double  connection  with  all  parts  of 
the  cerebral  cortex,  both  by  axones  from  the  cells  of  the  various 
nuclei  of  which  it  is  composed  (projection  system  of  the  thala- 
mus) and  by  axones  from  the  pyramidal  cells  of  all  parts  of 
the  cerebral  cortex.  Second,  it  is  connected  with  the  primary 
or  first  division  of  the  optic  tract  by  fibers  (axones  of  the 
ganglionic  cell  layer  of  the  retina)  which  end  about  the  cells  of 
the  pulvinar  and  external  geniculate  body.  Third,  it  has  a 
double  connection  with  the  occipital  lobe  by  axones  from  the 
cells  of  the  pulvinar  (optic  radiation),  which  end  about  the 
pyramidal  cells  of  the  cortex  of  the  occipital  lobe,  and  by  axones 
from  the  pyramidal  cells  of  that  lobe,  which  end  about  the  cells 
of  the  pulvinar.  Fourth,  the  anterior  nucleus  of  each  thalamus 
is  connected  with  the  corpus  albicans  by  the  fasciculus  thalamo- 
mammillaris,  or  bundle  of  Vicq  d'Azyr,  bringing  this  nucleus 
into  anatomic  relation,  through  the  fornix  fibers,  with  the 
hippocampal  and  uncinate  gyri.  Fifth,  the  fibers  of  the  len- 
ticular loop  end  chiefly  in  the  optic  thalamus,  and  connect  the 
lenticular  nucleus  (putamen  chiefly)  with  the  optic  thalamus. 
Sixth,  the  cells  of  the  ganglion  habenulse  give  rise  to  fibers 
which  form  the  fasciculus  retroflexus  of  Meynert.  This  con- 
nects the  thalamus  with  the  interpeduncular  ganglia.     Seventh, 

*It  is  very  probsble  that  the  fibers  of  the  fasciculus  retroflexus  terminate  in  arborizations 
about  the  cells  existing  in  the  interpeduncular  ganglion,  and  that  the  descending  part  of  the  tract 
which  descends  in  the  tegmentum  to  the  pons  and  medulla  is  the  axones  from  the  interpedun- 
cular ganglion  cells. 


REGION   OF    THE   THIRD   VENTRICLE.  259 

von  Monakow  has  shown  that  the  chief  part  of  the  median  fillet  or 
lemniscus  (interolivary  bundle  from  the  nuclei  of  Goll  and 
Burdach)  ends  about  the  cells  of  the  ventral  and  lateral  nuclei 
of  the  thalamus,  and  that  axones  from  these  latter  cells  pass 
through  the  posterior  part  of  the  internal  capsule  and  radiate 
toward  the  parietal  lobe,  forming  the  cortical  fillet  or  lemniscus. 
Eighth,  the  thalamus  is  connected  with  fibers  which  originate 
from  the  cells  of  the  nucleus  ruber  and  fibers  from  the  superior 
cerebellar  peduncles  ;  this  establishes  a  connection  between 
the  optic  thalamus  and  the  opposite  cerebellar  hemisphere. 
Ninth,  each  optic  thalamus  is  connected  with  the  caudate  nucleus 
by  a  fasciculus  of  fibers — the  stria  thalamica. 


THE     SUBTHALAMIC     REGION,     OR     STRATUM 
INTERMEDIUM. 

This  is  a  region  on  each  side  located  beneath  the  optic 
thalamus,  above  the  peduncles  of  the  cerebrum,  and  internal  to 
the  posterior  portion  of  the  internal  capsule.  This  region  con- 
tains an  intricate  maze  of  nerve-fibers, — the  zona  incerta, — which 
come  from  the  lenticular  nucleus,  the  internal  capsule,  and  the 
optic  thalamus  on  their  way  to  the  ganglia  located  in  this  region, 
which  ganglia  appear  wedged  in  between  the  extreme  posterior 
limb  of  the  internal  capsule  and  the  inferior  portion  of  the 
optic  thalamus.  These  ganglia  are  the  nucleus  ruber,  or  teg- 
mental nucleus  ;  the  subthalamic  nucleus,  or  Luys'  body  ;  and  the 
substantia' nigra,  or  locus  niger.  The  red  nucleus  appears,  on 
transverse  section,  as  a  spheric  shaped  body  located  beneath 
the  inner  portion  of  the  optic  thalamus,  internal  to  Luys'  body 
and  above  and  slightly  internal  to  the  substantia  nigra.  The 
subthalamic  nucleus,  Luys'  body,  is  a  lenticular  gray  mass 
resting  above  and  a  little  internal  to  the  crusta  ;  it  is  external  to 
the  red  nucleus  and  between  the  inferior  border  of  the  thalamus 
and  the  substantia  nigra.  The  substantia  nigra  is  located  just 
above  the  crus  cerebri,  and  continues  into  the  peduncle  of  the 
brain,  there  forming  an  intermediate  stratum,  which  serves  to 
separate  the  peduncle  into  a  ventral  portion,  or  crusta,  and  a 
dorsal  portion,  or  tegmentum. 


26o  CENTRAL   NERVOUS  SYSTEM. 

The  nucleus  hypothalamicus,  subthalamicum,  or  Luys'  body, 
is  of  a  dark  brownish  color,  lenticular  in  form,  and  spindle-shaped 
on  transverse  section.  It  is,  according  to  Koelliker,  9  to  10  mm. 
in  its  transverse,  3  to  5  mm.  in  its  dorsoventral,  diameter.  It 
is  inclosed,  save  at  its  mesial  surface,  by  a  capsule  of  fme 
medullated  nerve-fibers,  consisting  of  a  ventral  and  a  dorsal 
lamina.  The  nucleus  proper  consists  of  fine  medullated 
nerve-fibers,  having  in  their  meshes  a  number  of  angular  or 
spindle-shaped  cells  containing  much  granular  pigment  and 
possessing  many  protoplasmic  processes.  This  body  is  very 
rich  in  capillary  blood-vessels.  According  to  Stilling  and 
Koelliker,  some  of  the  fibers  from  the  optic  tract  (perforating 
fibers),  after  having  passed  through  the  crus  cerebri,  end  among 
the  nerve-cells  of  this  body.  It  is  quite  probable  that  these 
fibers  belong  either  to  Gudden's  or  Meynert's  commissure,  and 
are  not  an  essential  part  of  the  optic  tract.  This  statement 
seems  proved  by  an  observation  of  von  Monakow,  in  one  of 
whose  cases  there  was  complete  degeneration  of  the  entire 
optic  tract  while  Luys'  body  remained  absolutely  normal. 
Accordinof  to  this  observer,  manv  of  the  axones  from  the  cells 
of  Luys'  body  pass  through  the  crus  cerebri  and  enter  the 
corpus  striatum,  to  end  chiefiy  about  the  cells  of  the  outer 
division  of  the  lenticular  nucleus  or  putamen,  thus  establishing 
a  connection  between  this  body  and  the  lenticular  nucleus.  A 
commissure  exists  between  the  subthalamic  nuclei,  or  Luys' 
bodies,  consisting  of  nerve-fibers  from  two  sources  :  First,  fibers 
which  originate  in  the  subthalamic  nucleus  of  one  side,  which 
probably  pass,  after  decussating,  into  the  subthalamic  nucleus 
of  the  opposite  side  ;  second,  a  bundle  of  fibers,  first  described 
by  Forel,  existing  in  the  tegmentum,  lateral  to  the  red  nucleus. 
This  bundle,  accordinor  to  Forel,  consists  of  two  fasciculi — a 
ventral  and  a  dorsal.  The  ventral  fasciculus  (bundle  H^  of 
Forel)  consists  of  fibers  which  probably  originate  in  the  corpus 
mammillare  of  the  same  side  and  then  course  upward  and  along 
the  lateral  border  of  Luys'  body,  into  which  some  of  the  fibers 
enter,  while  the  majority  pass  through  the  crusta  into  the  in- 
ternal capsule.  The  fibers  of  the  dorsal  fasciculus  (bundle  H' 
of  Forel)  pass  into  the  basal  part  of  the  optic  thalamus. 


REGION   OF    THE   THIRD   VENTRICLE. 


261 


THE  RED  OR  TEGMENTAL  NUCLEUS  OF  STILLLNG. 

This  has  received  its  name  because  of  the  reddish  appear- 
ance it  presents  in  sections  of  fresh  brain,  this  color  being  due 
to  its  great  vascularity.  On  transverse  section  it  appears 
round,  while  in  sagittal  sections  it  has  an  elongated  oval  ap- 
pearance.    The  root-fibers  of  the  third  nerves  pass  vertically 


Fig.  131. — Section  of  Corpora  Quadrigemina.     Showing  cells  of  red  nucleus. 

Cox-Golgi  method. 


through  the  inner  portion  of  these  nuclei,  which  are  located 
deep  beneath  and  on  each  side  of  the  aqueduct  of  Sylvius, 
above  the  substantia  nigra  and  below  the  inner  portion  of  the 
thalami.  These  nuclei  are  surrounded  by  a  large  number  of 
meduUated  nerve-fibers,  which  form  for  them  a  sort  of  mantle, 
and  come  chiefly  from  the  cerebellar  peduncles.  Each  red 
nucleus  is  seen  to  be  composed  microscopically  of  a  very  thick 
tangle   or  plexus  of  nerve-fibers  and  collaterals,   having  inter- 


262  CENTRAL  NERVOUS  SYSTEM. 

spersed  amono-  them  a  number  of  triangular  multipolar  nerve- 
cells,  which  often  attain  a  very  great  size — 20  to  70  u  in  diam- 
eter. In  the  sheep  these  cells  are  possessed  of  from  two  to  six, 
rarely  more,  very  strong  dendritic  processes  of  great  length. 
They  frequendy  fork,  and  are  only  slighdy  beaded,  terminating 
free  or  in  a  bulbous  expansion.  The  axones  usually  come  off 
from  the  body  of  the  cells,  although  occasionally  they  may  be 
seen  to  arise  from  the  base  of  one  of  the  primary  dendritic 
trunks.  They  give  off  a  few  collaterals,  which  pursue  a  course 
dorsolaterally  toward  the  dorsal  tegmental  decussation. 

The  Connections  of  the  Red  Nucleus. — First,  with  the 
superior  cerebellar  peduncles.  The  experiments  of  Forel  and 
Gudden  prove  that  a  large  number  of  fibers  from  the  superior 
cerebellar  peduncle  of  one  side  end  about  the  cells  located  in 
the  posterior  portion  of  the  nucleus  ruber  of  the  opposite  side. 
F"orel  made  a  section  of  the  right  superior  cerebellar  peduncle 
of  a  rabbit,  and  found  resulting,  a  complete  atrophy  of  the  fibers 
of  the  peduncle  beyond  its  decussation  and  a  corresponding 
atrophy  of  the  posterior  portion  of  the  nucleus  ruber.  Gudden's 
experiment  differed  from  the  above  only  in  that  he  removed  the 
entire  left  cerebellar  hemisphere.  When  the  rabbit  matured,  a 
complete  atrophy  was  found  of  the  left  superior  cerebellar 
peduncle  and  posterior  portion  of  the  right  nucleus  ruber. 
Mahaim  has  proved  that  the  axones  from  the  cells  of  the 
middle  and  anterior  portion  of  the  nucleus  ruber  pass,  after 
decussating,  into  the  opposite  cerebellar  peduncle,  and  thence 
to  the  cerebellum.  This  nucleus,  according  to  Cajal,  receives 
collaterals  from  the  descendincr  teeniental  bundle,  which  bundle 
is  composed  of  axones  from  a  group  of  multipolar  cells  located 
in  the  lateral  portion  of  the  superior  layer  of  the  anterior  corpus 
quadrigeminum.  They  descend  in  curves,  decussate  in  the 
middle  line,  and  form  the  dorsal  or  fountain-like  decussation  of 
the  tegmentum  (Meynert).  They  then  continue  downward  on 
the  inner  side  of  the  lateral  fillet.  A  few  collaterals  and  axones 
from  Gudden's  commissure  pass  in  and  arborize  about  this 
nucleus.  It  is  connected  also  by  fibers  with  the  optic  thalamus 
and  lenticular  nucleus,  the  latter  fibers  passing  through  the 
internal  capsule. 


REGION   OF    THE   THIRD   VENTRICLE.  263 

THE    SUBSTANTIA    NIGRA     (LOCUS     NIGER;    INTERCALLATUM 

OF  SPITZKA). 

If  a  transverse  section  through  the  cerebral  peduncles  is  made 
at  any  point  beyond  the  ventral  border  of  the  pons,  a  dark-gray 
mass  of  increasing  size,  having  an  irregular  crescentic  outline, 
will  be  seen.  It  is  rather  thicker  on  its  inner  than  on  its  outer 
border,  and  consists  of  fine  nerve-fibers  and  numerous  multi- 
polar nerve-cells  of  a  spindle  shape  containing  granules  of  dark 
pigment ;  hence  its  name.  This  mass  serves  to  divide  each 
peduncle  into  a  ventral  and  a  dorsal  portion.  The  former,  which 
makes  up  about  one-third  of  the  bulk  of  each  peduncle,  receives 
the  name  crusta  ;  the  dorsal  part,  occupying  the  remaining  two- 
thirds,  is  called  the  teo-mentum. 


RETINA. 

In  order  fully  to  appreciate  the  relation  between  the  integral 
parts  of  the  retina  and  the  optic  paths,  and  the  course  taken  by 
light  impressions,  it  will  be  needful  to  precede  the  description  of 
the  optic  nerves  and  tracts  by  a  brief  description  of  the  histo- 
logic formation  of  the  retina.  The  retina  is  developed  embryo- 
logically  from  the  ventral  wall  of  the  optic  cup  by  a  multipli- 
cation of  its  cells.  It  is,  therefore,  an  outward  expansion  or 
growth  of  the  wall  of  the  primary  forebrain.  On  vertical  sec- 
tion the  retina  consists,  microscopically,  according  to  Schultze, 
of  eight -distinct  layers,  which  are,  from  within  outward,  as 
follows : 

1.  The  layer  of  the  optic  nerve-fibers. 

2.  The  layer  of  ganglionic  nerve-cells. 

3.  The  inner  molecular  layer. 

4.  The  inner  nuclear  layer. 

5.  The  outer  molecular  layer. 

6.  The  outer  nuclear  layer. 

7.  The  layer  of  rods  and  cones. 

8.  The  pigment  layer. 

The  retina  is  bounded  on  its  inner  side  by  a  very  delicate 
membrane^the  membrana  limitans  interna.     A  similar  mem- 


264 


CENTRAL  NERVOUS  SYSTEM. 


brane  exists,  lying  between  the  outer  nuclear  layer  and  the  layer 
of  rods  and  cones — the  external  limiting  membrane. 

I.  The  Laye?'  of  Optic  Nerve-Jibe?^ s. — This  layer  consists  of  a 
large  number  of  nerve-fibers,  mostly  axones  from  the  gangli- 
onic cells  of  the  layer  above,  and  whose  course  is  centripetal, 


Outer  or  clioroid  surface. 


I'^^'    Layer  of  pigment  cells. 
~ -J  Layer  of  rods  and  cones. 
..  Membrana  limilans  externa. 
6.  (Kiter  nuclear  layer. 

5.  Outer  molecular  layer. 
4.  Inner  nuclear  layer. 


ner  molecular  layer. 


I  2,  Layer  of  nerve-cells. 

L   Layer  of  nerve  fibers. 
ZT   ■    •  Membrana  limitans  interna. 
Inner  or  vitreous  surface. 
Fig.  132. — Diagrammatic  Section  of  the  Human  Retina. — {Sc/iu/tze.) — {After  Quain.) 

forming  a  large  part  of  the  fibers  of  the  optic  nerve.  Some  of 
the  fibers  of  this  layer  course  (centrifugally)  through  the  gang- 
lionic cell  layer,  and  terminate  either  in  the  inner  molecular 
layer  or  in  the  fourth  or  inner  nuclear  layer,  among  the  bipolar 
cells. 

2.    The  Layer  0/  Ganglionic  Ceils. — The  ganglionic  cell  layer 


REGION   OF    THE   THIRD   VENTRICLE. 


265 


is  located  just  external  to  the  layer  of  optic  nerve-fibers.  It 
consists,  save  in  the  region  of  the  macula,  of  a  single  stratum 
of  multipolar  nerve-cells.  Each  cell  has  a  single  axis-cylinder 
process,  or  axone,  whose  course  is  central,  and  these  axones, 
with  others,  proceed  inward  to  form  most  of  the  fibers  of  the 
optic  nerve.  The  peripheral  process  or  dendrite  becomes 
branched,  and  terminates  in  the   inner  molecular  layer,  there 


Rods  and  cones 


\'isual  cell 


tenial  molecu- 
ayer 


er  of  gangli- 
cells 

er  of  optic 
fibers 


Fig.  133. — Section  through  the  Retina  of  a  Mammal  to  show  Layer  of  Hori- 
zontal Cells  of  the  External  Molecular  Layer  and  the  Spongioblasts  of 
THE  Internal  Molecular  Layer. — i^After  Ramon y  Cajal.) 


commingling  with    the    central  processes  of  the    bipolar    cells 
of  the  inner  nuclear  layer. 

3.  The  Inner  Molec2iIar  Layer. — This  layer  consists  chiefly 
of  the  dendrites  of  the  ganglionic  cells  of  the  second  layer, 
together  with  the  arborizations  of  the  central  processes  of  the 
bipolar  cells  of  the  inner  nuclear  layer.  This  layer  contains,  in 
addition,  a  number  of  cells  which  resemble  young  neuroglia 
cells  (spongioblasts),  but  which,  according  to  Ramon  y  Cajal, 
are  nerve-cells.  Owing  to  the  inability  to  find  axis-cylinder 
processes,  he  calls  them  amacrine  cells. 

4.  The  imier  nuclear  layer  is   made   up  mainly  of  round   or 


266  CENTRAL  NERVOUS  SYSTEM. 

oval-shapcd  cells,  each  with  two  processes — a  central  and  a  per- 
ipheral. The  peripheral  process  or  axone,  which  is  exceedingly 
fine,  courses  inward  to  the  inner  molecular  layer,  where  it 
terminates  in  an  arborization  about  a  dendritic  process  of  a 
ganglionic  cell.  The  peripheral  process  or  dendrite  of  these 
bipolar  cells  is  quite  thick,  and  continues  outward  into  the  outer 
molecular  layer,  where  it  breaks  up  into  several  fine  branches, 
producing  an  arborization  which  comes  in  contact  with  an 
arborization  from  a  central  process  or  axone  of  a  visual  cell 
existing  in  the  outer  nuclear  layer. 

5.  The  outer  or  external  molecular  layer  is  not  nearly  so  thick 
as  the  inner  molecular  layer,  and  consists  almost  entirely  of  the 
arborizations  of  the  axones  of  the  visual  cells  of  the  outer 
nuclear  layer,  together  with  the  termination  of  the  dendrites  of 
the  bipolar  cells  of  the  inner  nuclear  layer  and  the  horizontal 
cells, '=' 

6.  TJic  Outer  Nuclear  Layer. — This  is  the  layer  of  visual 
cells  (Van  Gehuchten),  These  cells  are  oval  or  round  in  shape, 
and  are  bipolar.  Their  central  processes  or  axones  proceed 
inward,  and  terminate,  either  in  arborizations  or  in  enlarged  or 
thickened  extremities,  in  the  outer  molecular  layer  about  the 
dendrites  of  the  bipolar  cells  of  the  inner  nuclear  layer.  The 
peripheral  processes  of  these  cells  are  the  rods  and  cones  of  the 
retina,  which  may  be  likened  to  the  dendrites  of  other  nerve- 
cells.  The  axones  of  the  visual  cells  whose  dendrites  form  the 
rods,  end  in  slight  thickenings  or  in  clubbed  extremities,  while 
the  axones  of  the  cells  whose  dendrites  form  the  cones  terminate 
in  arborizations. 

7.  The  Layer  of  Rods  and  Coiies. — The  rods  and  cones  are 
the  peripheral  processes  or  dendrites  of  the  visual  cells  ;  they 
are  arranged  in  a  palisade-like  manner  throughout  the  whole 
extent  of  the  retina,  between  the  external  limiting  membrane 
and  the  pigment  layer.  The  rods  are  much  more  numerous 
than  the  cones,  and  are  cylindric  in  form.     The  cones  are  conic 


*  These  horizontal  cells,  according  to  Van  Gehuchten,  are  found  in  the  external  molecular 
layer.  Their  protoplasmic  processes  (dendrites)  are  in  relation  with  the  axones  of  the  visual 
cells,  while  their  axis-cylinders  pass  horizontally  through  the  molecular  layer  to  end  in  fine 
ramifications  about  the  axones  of  visual  cells  at  variable  distances. 


REGION   OF    THE   THIRD   VENTRICLE. 


267 


in  shape,  and  are  shorter  and  broader  than  the  rods.  Both 
the  rods  and  cones  are  divisible  into  outer  and  inner  segments. 
In  the  case  of  the  rods,  this  division  is  at  about  the  middle  of  its 
length,  while  in  the  cones  it  is  at  the  junction  of  the  tapering 
point  with  the  expanded  part.  The  outer  segments  of  the  rods 
are  cylindric,  and  are  transversely  and  longitudinally  striated  ; 
they  terminate  in  the  pigment  or  outer  layer.  The  outer  seg- 
ments of  the  rods   are   supposed  to  occasion  the   purplish-red 


Layer  of  rods  and  cones. 


Externa]  granular  layer  wiih 
visual  cells. 


External  molecular  layer. 


Internal  granular  layer  of 
bipolar  cells. 


Internal  molecular  layer. 

Layer  of  ganglionic  cells. 

Layer  of  optic  nerve-fibers. 
Fig.  134. — The  Essential  Elements  in  the  Retina  of  a  Tiog.— {After  Van  Ge/utc/iten.) 


color  of  the  retina.  The  outer  segments  of  the  cones  are 
spindle-shaped,  and  taper  to  a  blunt  point,  which  also  ends  in  the 
pigment  layer ;  they  are  only  striated  transversely.  The  inner 
segments  of  both  the  rods  and  cones  are  continuous,  through 
the  membrana  limitans  externa,  with  the  peripheral  processes  of 
the  visual  cells. 

8.    The  Pigment  Layer  of  the  Retina. — This,  the  outer  layer 
of  the  retina,  is  composed  of  a  single  layer  of  hexagonal  cells 


268 


CENTRAL  NERVOUS  SYSTEM. 


separated  by  a  distinct  amount  of  intercellular  substance.  The 
outer  surface  of  these  cells  is  slightly  convex,  and  is  in  contact 
with  the  inner  layer  of  the  choroid.  Their  inner  surface  rests 
against  the  layer  of  rods  and  cones  with  which  these  cells  come 
in  contact,  either  by  sending  out  slight  protoplasmic  processes, 
which  pass  between  the  rods  and  cones,  or  by  contact  with  the 
inner  surface  of  their  cell-body.  Each  of  these  cells  possesses 
an  outer  clear  zone  containing  an  unpigmented  nucleus,  and  an 
inner  zone  filled  with  dark  pigment  granules  (Figs.  132,  133, 
and  134). 

int.qen:  h.       sup.  hrach. 
puluiruir  \  'l/^  Itmch. 

eup.  {fuatl.h. 


opt.  frrt«t 
an^.peri:  sp. 


post.fjfr^  sp, 
Corp.  aU>. 

-lub.cin. 

ipi? —  opl.f  orrun.. 


cpfc.  nerve 


Fig.  135. — The  Origin  anu  Relation  of  the  Optic  Tract. — (G^.  D.  Thane.) — 

{From  Quain.) 

The  parts  are  viewed  from  below  the  mid-brain,  having  been  divided  transversely  immediately 

above  the  pons,  and  the  ix)ns,  cerebellum,  and  medulla  oblongata  are  removed. 


THE    COURSE    OF    THE    OPTIC    NERVES    AND   TRACTS. 

The  optic  nerve  is  protected  by  a  strong  outer  sheath  of 
dura  mater,  which  is  continuous  with  the  sclerotic  coat  of  the 
eyeball.  A  process  of  pia  mater  closely  invests  the  nerve 
internally,  and  between  the  two  exists  the  arachnoid  membrane, 
the  outer  surface  of  which  is  adherent  to  the  dura.  The  space 
between  the  arachnoid  communicates  with  the  oreneral  sub- 
arachnoid  space.  The  individual  nerve-fibers  of  which  the  optic 
nerve  consists  are  not  surrounded  by  a  sheath  of  Schwann. 

Each  optic  nerve  contains  an  enormous  number  of  nerve- 
fibers  (400.000  to  450,000  Salzer),  which  may  be  divisible 
into    centripetal    and    centrifugal    tracts    of  fibers.       The    cen- 


REGION   OF    THE   THIRD   VENTRICLE. 


269 


tripetal  fibers  of  the  optic  nerve  are  the  central  processes 
or  axones  of  the  multipolar  or  ganglionic  cells  of  the  second 
layer  of  the  retina.  The  peripheral  processes  or  dendrites 
of  these  cells,  as  we  have  seen,  arborize  about  the  axones 
of  the  bipolar  cells  of  the  retina ;  the  dendrites  of  these 
latter  cells  terminate  about  the  axones  of  the  visual  cells,  whose 
peripheral  processes  are  the  rods  and  cones.  There  is  thus 
established  a  conducting-  medium  throuo;h  the  retina  continuous 

o  o 


Fig.  136.— Microphotograph  through  Optic  Thalamus  of  a  Sheep.     Showing  fibers 
from  optic  nerve  terminating  about  stellate  cells.      Method  of  Berkley. 

with  the  optic  nerve  ;  each  optic  nerve  then  passes  backward 
and  slightly  inward  through  the  opdc  foramen  to  the  region 
immediately  in  front  of  the  tuber  cinereum,  where  it  unites  with 
its  fellow  to  form  the  optic  commissure  or  chiasm.  The  greater 
part  of  the  fibers  of  each  nerve  decussate  with  those  of  the 
opposite  side  to  join  the  opposite  opdc  tract,  but  the  remainder 
continue  backward  in  the  lateral  pordon  of  the  chiasm  without 
decussadng,  passing  into  the  optic  tract  of  the  same  side.     The 


270  CENTRAL  NERVOUS  SYSTEM. 

crossed  fibers  come  from  the  cells  of  the  nasal  half  of  each 
retina,  while  the  uncrossed  come  from  the  cells  of  the  temporal 
half  of  each  retina. 

Each  optic  nerve  contains  a  fasciculus  of  fibers  which  take 
their  origin  from  the  resfion  of  the  macula  of  the  retina  and 
pass  into  the  optic  tract  of  the  same  and  opposite  sides.  The 
fibers  of  this  fasciculus  which  pass  into  the  optic  tract  of  the 
same  side  probably  come  from  the  temporal  side  of  the  macula, 
while  those  that  decussate  and  pass  into  the  optic  tract  of  the 
opposite  side  doubtless  come  from  the  nasal  side  of  the 
macula.  This  bundle  of  fibers  is  triangular  on  transection,  and 
occupies,  at  first,  the  inferior  portion  of  the  optic  nerve ;  as  the 
nerve  passes  through  the  optic  foramen,  it  becomes  more  cen- 
trally located  ;  just  before  reaching  the  optic  chiasm  it  occupies 
the  dorsomesial  part  of  the  nerve.  In  the  optic  tract  it  is  again 
centrally  placed.  Each  optic  tract,  then,  contains  the  fibers 
from  the  nasal  half  of  the  retina  of  the  opposite  eye  and  from 
the  temporal  half  of  the  retina  of  the  same  eye.  The  optic 
tract  then  continues  backward  under  the  cover  of  the  temporal 
lobe,  passing  around  the  crus  cerebri,  where  it  is  separated  by  a 
groove  into  two  distinct  fasciculi  or  bundles — a  lateral  or  ex- 
ternal, and  a  mesial  or  internal.  The  mesial  or  internal  fascic- 
ulus is  not  concerned  with  vision,  but  is  connected  \vith  the 
internal  geniculate  body  and  posterior  corpus  quadrigeminum, 


Fig.  137. — Diagram  of  the  Corpora  Quadrigemina  Anterior,  CQA,  showing 
THEIR  Connections. — [After  M.  A.  Starr.) 
On  the  I'iglit  of  the  tigiire  the  superficial  and  deep  masses  of  gray  matter  are  shown,  pulv. 
Pulvinar  of  the  optic  thalamus,  pn.  Posterior  nucleus  of  the  optic  thalamus  lying  between 
the  corpus  geniculatum  externum,  cge,  and  the  corpus  geniculatum  internum,  cgi.  I  C. 
Internal  capsule.  /".  Fillet.  R  yV'.  Red  nucleus  of  tegmentum.  P  E  D.  Peduncle  of 
cerebrum,  sn.  Substantia  nigra.  O  T.  Optic  tract.  A'.  Optic  chiasm.  //.  Optic  nerve. 
I,  2.  Fibers  from  retina  to  pulvinar  of  ojHic  thalamus  (I,  centripetal)  (2,  centrifugal). 
7  and  8.  Fibers  between  the  optic  thalamus  and  occipital  cortex.  3  and  4.  Fibers  between 
the  retina  and  the  corpus  geniculatum  externum.  9  and  ID.  Corresponding  fibers  to 
occipital  lobe.  5  and  6.  Fibers  between  the  retina  and  corpus  quadrigeminum  anterior.  II 
and  12.  Corresponding  fibers  to  the  occipital  cortex.  13.  Cell  of  the  superficial  gray 
matter  of  the  CQA  sending  fiber  to  the  nucleus  of  the  third  nei-ve,  16.  14.  Cell  of  the 
deep  gray  matter  o{  C  Q  A  sending  fiber  to  third  nerve  nucleus.  15.  Cell  of  the  deep  gray 
matter  o{  C  Q  A  sending  fiber  to  fillet.  17.  Fiber  from  the  red  nucleus  terminating  about 
14.  18.  Fiber  from  fillet  terminating  about  13.  O  L.  Occipital  lobe  of  the  brain,  with 
its  cortex,  containing  both  cells  and  terminal  brushes  of  the  visual  tract. 


Fig.  137. — Diagram  ok  the  Corpora  Quadrigemina  Anterior. 


271 


REGION   OF    THE   THIRD   VENTRICLE.  273 

and  is  a  part  of  Gudden's  commissure.  The  lateral  bundle  is 
the  true  optic  tract,  and  passes  into  the  primary  optic  ganglia, 
which  are  the  external  geniculate  body,  the  pulvinar  of  the  optic 
thalamus,  and  the  anterior  or  superior  corpus  quadrigeminum, 
entering  the  latter  by  way  of  its  arm  or  brachium.  The  fibers 
of  the  opdc  tract  terminate  in  fine  end  brushes  about  the  nerve- 
cells  of  the  superficial  and  deep  layers  of  the  lateral  or  external 
geniculate  body.*  In  the  optic  thalamus  they  terminate  chiefly 
about  the  nerve-cells  of  the  posterior  portion  (pulvinar).  In  the 
anterior  corpus  quadrigeminum  they  form  the  superficial  layer 
of  white  fibers,  terminating  free  or  in  brush-like  expansions  about 
its  nerve-cells.  From  the  cells  of  the  primary  optic  ganglia 
new  axones  arise  which  issue  from  the  outer  side  of  the 
thalamus  and  pass  through  the  extreme  posterior  end  of  the 
internal  capsule ;  they  then  curve  backward  around  the  posterior 
horn  of  the  lateral  ventricle  and  radiate  through  the  centrum 
semiovale  (optic  radiation  of  Gratiolet)  to  the  cortex  of  the 
occipital  lobe,  ending  chiefly  in  the  cuneus  and  the  parts  ad- 
jacent to  the  calcarine  fissure. 

The  centrifugal  fibers  of  the  first  division  of  the  optic  nerve 
come  from  the  cells  of  the  primary  optic  ganglia  and  pass  to 
the  retina.  The  centrifugal  fibers  for  the  second  division  of  the 
opdc  tract  are  the  axones  of  the  pyramidal  cells  of  the  occipital 
cortex.  They  end  about  the  cells  of  the  primary  optic  ganglia. 
There  is  thus  established  a  condnuous  centrifugal  fasciculus  of 
fibers  for  the  opdc  tract  from  the  occipital  cortex  to  the  retina 
(von  Monakow). 

THE  CONNECTIONS  OF  THE  OPTIC  TRACT. 
Although  the  exact  path  of  connection  between  this  tract  and 
the  nuclei  of  the  motor  nerves  of  the  eye  is  not  definitely  known, 
it  is  probable  that  it  may  be  through  the  axone  of  the  cells  of 
the  anterior  corpus  quadrigeminum  on  each  side,  which,  pro- 
ceding  downward,  join  the  posterior  longitudinal  bundle,  and 
thus  reach  the  region  of  the  nuclei  of  the  third,  fourth,  and  sixth 


*  The  external  geniculate  bodies   receive    exclusively  .the   fibers  coming  from  the  macula 

lutea. 

18 


274 


CENTRAL  NERVOUS  SYSTEM. 


nerves.  According  to  Koelliker.  the  axones  from  these  cells 
pass  directly  or  by  their  collaterals  to  the  central  gray  matter 
around  the  Sylvian  aqueduct,  and  there  arborize  about  the  cells 
of  the  third  nerve  nuclei.  According  to  Darkschewitsch,  a 
bundle  of  fibers  leaves  the  mesial  portion  of  the  optic  tract, 
pierces  the  thalamus,  and  reaches  the  oculomotor  nucleus  through 
the  ventral  portion  of  the  posterior  commissure.  This  bundle, 
he  believes,  may  complete  the  reflex  arc  by  which  a  connection 
is    made    between    the    retina    and    the  ventral   portion   of   the 


Fio.  138. — HoRizoNiAL  Section  through  the  Optjc  Chiasm  of  a  Child. — [After 

Koelliker. ) 

CM.   Meynerfs  commissure.      Ah.   Optic  nerve.      Tr.o.  Oplic  tract,     v.  Ventral  concavity  of 

chiasm. 


third  nerve  nucleus,  which,  according  to  Kahler  and  Pick,  govern 
the  contraction  of  the  pupil.  The  optic  nerves  are  probably  con- 
nected through  their  primary  ganglion,  by  means  of  the  median 
fillet  or  lemniscus,  with  the  medulla  oblongata  and  the  spinal  cord. 
(See  Fig.  137.) 

THE  OPTIC  CHIASM. 
This  commissure  is  oblong  in  shape,  its  longest  diameter  being 
from  10  to  12  mm.;  it  rests  in  the  optic  groove  of  the  sphenoid 
bone.     On  each  side  the  anterior  perforated  space  and  internal 


REGION   OF    THE   THIRD   VENTRICLE. 


275 


carotid  artery  are  located.  A  litde  above,  and  anteriorly,  lies 
the  lamina  cinerea  ;  posteriorly,  is  the  tuber  cinereum,  with  the 
infundibulum.  The  middle  portion  of  the  chiasm  is  occupied  by 
fibers  of  the  optic  nerves,  which  decussate  and  pass  to  the  oppo- 
site sides.  Its  lateral  portions  are  occupied  by  those  fibers  of 
the  optic  nerves  which  do  not  decussate.  The  posterior  portion 
of  the  chiasm  is  occupied  by  the  so-called  "inferior  commissure 
of  Gudden."  *  This  commissure  consists  of  a  bundle  of  fibers 
for  each  side,  which  bundle,  after  decussating,  joins  the  optic 
tract,  forming  its  mesial  portion.     It  then  passes  to  the  internal 


fj*  dn. 


Lntl         C I 


Fig.  139. — Frontal  Section  through  the  Interbrain. — {After  Koellikei'.) 
Ch.  Commissure  of  the  hypothalamic  nuclei.  F7n.  Fasciculus  thalmomammillaris  Vicq  d' Azyr. 
Th.o.  Optic  thalamus,  dm.  Stratum  zonale  of  hypothalamic  nuclei.  H'^.  Field  I  of 
Forel.  Lml.  Lateral  medullary  lamina  of  optic  thalamus.  C.i.  Internal  capsule.  I,  II, 
and  ///.  The  three  divisions  of  the  lenticular  nucleus.  Tr.o.  Optic  tract.  Pp.  Pes 
peduncli.  H'^ .  Field  2  of  Forel.  CL.  Luys'  body.  Z.i.  Zona  incerta  of  Forel.  Cm. 
Corpus  mammillaria. 

geniculate  body.  According  to  some  authors,  it  continues  by  way 
of  the  posterior  arm  or  brachium  into  the  posterior  corpus  quad- 
rigeminum.  According  to  Obersteiner,  part  of  this  bundle 
passes  by  way  of  the  lenticular  loop  (ansa  lenticularis)  into  the 
lenticular  nucleus,  thus  forming  a  crossed  connection  between 
that  nucleus  and  the  internal  geniculate  body. 

Gudden's  commissure   also    contains    a    fasciculus    of  fibers 


*  Hannover  believes  that  a  fasciculus  of  fibers  exists  on  each  side  which  is  located  in  the 
most  ventral  part  of  the  optic  chiasm,  and  that  they  form  a  commissure  whose  function  is  to 
associate  both  retinae  together. 


276  CENTRAL  NERVOUS  SYSTEM. 

occupying-  its  innermost  part  which  join  the  outermost  part  of  the 
crus  cerebri.  These  fibers  probably  come  from  the  cortex  of 
the  occipital  and  temporal  lobes.  This  commissure  was  dis- 
covered by  Gudden,  who  enucleated  the  eyes  in  very  young 
animals  and,  as  a  result,  found  that  while  both  optic  nerves  and 
the  primary  optic  ganglia  were  completely  degenerated,  the 
internal  geniculate  bodies  and  a  fasciculus  of  fibers  occupying  the 
posterior  portion  of  the  chiasm,  which  showed  no  degenerative 
chanees,  remained,  and  hence  could  have  no  connection  with 
vision. 

Dorsal  to  Gudden's  commissure  is  a  fasciculus  ot  fibers  called 
Meynert's  commissure.  It  has  no  connection  with  the  optic 
tract,  and  is  not  concerned  with  vision.  Its  supposed  origin  is 
from  collections  of  spindle  cells  located  on  each  side  of  the 
tuber  cinereum.  These  collections  of  cells  form  the  basal  optic 
ganglia.  The  axones  of  the  cells  pass  in  curves  into  the  crus 
cerebri,  and  probably  terminate  about  the  cells  ot  the  subthalamic 
or  Luys'  nucleus  (Fig.  138). 


THE  PITUITARY  BODY. 

This  gland,  also  called  hypophysis  cerebri,  has  been  described 
on  page  323.  It  is  divided  into  two  portions  or  lobes  :  an  ante- 
terior  or  glandular  portion,  which  is  the  larger,  partially  sur- 
rounding the  posterior,  which  is  called  the  infundibular  lobe. 
Between  the  two  lobes  is  a  closed  canal,  lined  with  epithelium. 
The  glandular  portion  is  developed  from  the  ectoderm  of  the 
buccal  cavity.  The  posterior  or  infundibular  lobe  is  continuous 
with  the  infundibulum,  and.  like  that  body,  is  developed  as  an 
outgrowth  from  the  floor  of  the  third  ventricle.  According  to 
Berkley,  who  has  made  an  exhaustive  study  of  the  anatomy  of 
this  gland,  the  anterior  portion  contains  nerves  which  belong  to 
the  sympathetic  system  only.  Some  are  fine  varicose  fibers, 
with  numerous  ramifications  coming  off  from  the  main  stem  at 
right  or  slightly  obtuse  angles.  Others  follow  the  course  of 
the  arteries,  and  give  off  from  the  main  stem  branches  which 
course  irregularly  through  the  gland  substance,  crossing  over  or 
accompanying  the   large  venous   channels   in   the  septa,   to   be 


REGION   OF    THE   THIRD   VENTRICLE. 


277 


distributed  upon  the  coils  of  the  epithehal  cells  of  the  follicles, 
there  terminating  in  clubbed  extremities.  No  nerve-cells  are 
found  in  the  anterior  portion  of  the  gland.  In  the  infundibular 
or  posterior  lobe  of  this  gland  are  three  distinct  parts  :  First, 
an  outer  lamina  of  ependymal  cells,  arranged  in  several  layers, 
which  are  separated  by  dehcate  connective-tissue  trabeculae 
from  the  surrounding  capsule.  Secondly,  an 
inner  layer  of  epithelial  cells  of  a  secretory  type, 
often  arranged  into  distinct  acini,  which  latter 
are  separated  by  connective-tissue  bands  carry- 
ing blood-vessels.  The  acini  occasionally  coal- 
esce, forming  small  cavities,  which  sometimes 
contain  colloid  material.  Thirdly,  a  central  re- 
gion containing  small  round  and  polygonal  cells 
separated  by  connective  tissue,  together  with  a 
few  spindle  or  pear-shaped  cells.  The  nerve- 
cells  are  found  only  in  the  ventral  portion  of  the 
posterior  lobe.  They  are  divided  into  cells  pos- 
sessing one  neuraxone  (of  which  there  are  two 
forms — a  large  and  a  small  oval  or  pyramidal) 
and  a  second  form — those  which  possess  two  or 
more  neuraxones.  The  large  pyramidal  cells 
of  the  first  class  possess  many  strong  branching 
dendrites,  which  terminate  in  beautiful  feathery 
tufts.  The  axones  give  off,  close  to  the  cell- 
bodies,  a  few  collaterals,  and  terminate  by 
breaking  up  into  a  number  of  fine  branches, 
some  of  ,which  are  lost  about  other  nerve-cells, 
while  others  end  in  networks  among  the  epi- 
thelial cells  along  the  border  of  the  lobe. 
The  small  pyramidal  cells  differ  from  those 
just  described,  in  that  they  possess  dendrites, 
all  of  which,  save  one,  are  short  and  have  hair-like  processes  on 
the  main  stem  close  to  the  cell-body,  and  terminate  free  in 
clubbed  extremities.  The  cells  of  the  second  group  are  chiefly 
flask-shaped,  and  are  widely  distributed.  They  each  possess 
from  three  to  four  dendrites,  which  grow  gradually  finer  and 
terminate   free.     These  cells  possess  from  two  to  four  very  fine 


Fig.  140. — Sagittal 
Section  of  the 
Pituitary      Body 

AND         InFUNDIBU- 

LUM  WITH  Adjoin- 
ing Part  of 
Third  Ventricle. 
■ — [Schwa Ibe,  frovi 
Qiiaiti.) 
a.  Anterior  lobe,  a' . 
A  projection  from  it 
toward  the  front  of 
the  infundibulum. 
b.  Posterior  lobe 
connected  by  a  stalk 
with  the  infundibu- 
lum, i.  I.e.  Lamina 
cinerea.  0.  Right 
optic  nerve.  ch. 
Section  of  optic 
chiasm,  r.o.  Recess 
of  ventricle  above 
the  chiasma.  an. 
Corpus  mammillare. 


278 


CENTRAL  NERVOUS  SYSTEM. 


axis-cylinders,  which  apparently  terminate  about  similar  cells. 
In  addition,  there  are  several  forms  of  cells  found  in  various 
parts  of  the  gland,  such  as  small  flask-shaped  and  pyramidal 
cells  found  in  the  central  part  of  the  gland,  small  spheric  cells 
possessing  dendritic  processes  which  cover  a  large  space,  and 


,j^v 


Fig.  141. — Examples  of  Some  of  the  Various  Forms  of  Pyramidal  Cells  Found 
IN  THE  Ventral  Part  of  the  Posterior  Lobe  of  the  Pituitary  Body. — {After 
Berkley. ) 

5  and  6.  Irregularly  pyramidal  or  oval  cells  with  numerous  dendrites  terminating  in  feathery 
arborizations  and  a  single  neuraxone.  II.  Pyramidal  cell  with  very  long  apical  dendrite. 
12.    Pyramidal  cell  with  dendrites  terminating  in  feathery  tufts. 


spheric  cells  whose  processes  end  in  tufts  of  fine  filaments. 
Most  of  the  axones  from  these  various  cells  course  upward 
toward  the  infundibulum,  but  Berkley  was  unable  to  follow  any 
of  the  fibers  into  that  body  (Figs.  140  and  141). 


REGION   OF    THE   THIRD   VENTRICLE.  279 

THE  TUBER  CINEREUM. 

The  tuber  cinereum  is  an  elevation  of  gray  matter  between 
the  corpora  mammillaria  behind,  and  the  optic  commissure 
in  front,  to  which  it  is  attached.  It  is  continuous  anteriorly  with 
the  lamina  cinerea.  From  its  middle  portion  extends  down- 
ward and  slightly  forward  a  conic  process, — the  infundibulum, — 
which  is  connected  with  the  posterior  lobe  of  the  pituitary  body. 
The  tuber  and  infundibulum  correspond  to  a  recess  in  the  middle 
portion  of  the  third  ventricle. 


THE  INFUNDIBULUM. 

Berkley  has  shown  that  the  infundibular  walls  are  very  rich  in 
neuroglia  elements.  These  cells  consist  of  two  chief  varieties  : 
Elongate  or  slightly  pyramidal  forms,  which  begin  just  beneath 
the  ventricular  surface  and  extend  almost  through  the  wall  to 
near  its  outer  margin  ;  they  break  up  into  a  few  fine  branches, 
which  are  occasionally  clubbed.  The  second  type  is  a  large 
spheric  neuroglia  cell  with  processes  radiating  from  all  parts  of 
the  cell-body.  This  form  is  found  throughout  the  infundibular 
wall,  but  is  more  abundant  on  its  inner  portion.  The  nerve-cells 
are  all  multipolar,  mostly  pyramidal  in  shape,  and  possses  one 
or  more  neuraxones,  which  are  sparse  in  comparison  with  the 
neuroglia  elements. 


CHAPTER  VII. 
THE  MEMBRANES  OF  THE  BRAIN. 

The  membranes  that  surround  the  brain  are  three  in  number: 
(i)  An  external  fibrous  membrane — the  dura  mater;  (2)  an  in- 
ternal vascular  membrane — the  pia  mater  ;  (3)  a  very  delicate 
membrane  situated  between  the  pia  and  dura — the  arachnoid 
membrane. 

DURA  MATER. 

The  cerebral  dura  mater  is  a  tough,  rather  thick,  inelastic 
membrane,  possessing  a  rough  external  or  periosteal  surface, 
and  a  smooth,  Mistenine,  internal  surface  lined  with  flattened 
endothelium.  The  fibrous  tissue  of  which  the  dura  mater  is 
composed  consists  of  two  layers  or  laminae,  an  outer  and  an  inner, 
which  are  inseparable  for  the  greater  part  of  their  extent ;  but  in 
certain  localities  they  separate,  forming  channels  which  consti- 
tute the  venous  sinuses.  These  channels  are  lined  with  endo- 
thelium continuous  with  that  of  the  inner  coats  of  the  veins. 
The  external  or  outer  surface  of  the  dura  forms  the  periosteum 
(endocranium)  of  the  internal  surface  of  the  skull.  In  the  adult 
the  dura  is  rather  loosely  attached  to  the  bones  of  the  cranial 
vault,  save  along  the  line  of  the  sutures,  where  it  is  intimately 
adherent  by  many  small  fibrous  processes  and  blood-vessels 
which  penetrate  the  bones.  It  is  also  firmly  attached  at  the  base 
of  the  skull,  and  gives  off  tubular,  fibrous  prolongations  which 
blend  with  areolar  sheaths  of  the  cranial  nerves  as  they  pass 
throuijh  the  various  basal  foramina,  formino-  for  these  nerves 
tough,  fibrous  envelopes,  which  are  continuous  with  the  peri- 
cranium. On  the  outer  side  of  each  cavernous  sinus  the  Gas- 
serian  ganglion  is  located,  in  a  space  between  the  dural  laminae, 

called  the  cavum  Meckelii.    The  dura  is  closely  adherent  around 

2S0 


THE    MEMBRANES    OF   THE    BRAIN.  281 

the  margin  of  the  foramen  magnum,  and  becomes  continuous 
through  this  foramen  with  the  dura  mater  surrounding  the 
spinal  cord. 


PROCESSES   OF  THE   CEREBRAL   DURA   MATER. 

The  dura  mater  sends  the  following  processes  into  the 
interior  of  the  skull :  the  falx  cerebri,  the  tentorium  cerebelli, 
and  the  falx  cerebelli. 

The  falx  cerebri,  or  processus  falciformis  major,  is  a 
strong,  curved  process  of  dura  mater,  sickle-like  in  shape,  which 
is  located  in  the  great  longitudinal  fissure,  the  convexity  being 
above,  the  concavity  below.  Its  narrow  anterior  part  is  attached 
to  the  crista  galli  of  the  ethmoid  bone  ;  its  broad  posterior  part 
is  connected  with  the  middle  of  the  upper  surface  of  the  ten- 
torium cerebelli,  along  which  line  of  attachment  the  straight 
sinus  runs.  Its  convex  superior  surface  has  a  rather  broad 
attachment  along  the  middle  line  of  the  under  surface  of  the 
frontal,  parietal,  and  occipital  bones  as  far  back  as  the  internal 
occipital  protuberance.  Between  the  laminae  of  this  process 
exists  a  large  venous  space — the  superior  longitudinal  sinus. 
Its  inferior  concave  surface  is  free,  and  lodges  the  inferior 
longitudinal  sinus  ;  behind,  it  approaches  the  corpus  callosum. 

The  Tentorium  Cerebelli. — The  tentorium  cerebelli  is  a 
transverse  arched  process  of  the  dura  mater  located  between 
the  inferior  surface  of  the  occipital  lobes  and  the  superior 
surface  of  the  cerebellum,  which  latter  surface  it  covers.  The 
occipital  lobes  are  supported  by  it,  being  thus  prevented 
from  exerting  pressure  on  the  cerebellum.  The  tentorium  is 
decidedly  convex  along  its  median  portion,  forming  a  ridge  to 
which  is  attached  the  posterior  border  of  the  falx  cerebelli. 
This  process  gradually  inclines  downward  in  all  directions 
toward  its  circumference,  following  the  form  of- the  superior 
surface  of  the  cerebellum,  and  forming  over  it  a  roof-like 
structure.  The  convex  posterior  border  of  the  tentorium  is 
attached  to  the  transverse  ridges  of  the  inner  surface  of  the 
occipital  bone,  and  here  separates  to  form  the  lateral  sinuses. 
In  front  it  is  united  to  the  superior  borders  of  the  petrous  por- 


2S2 


CENTRAL  NERVOUS   SYSTEM. 


tions  of  the  temporal  bones,  inclosing  the  superior  petrosal 
sinuses.  At  the  ape.\  of  the  petrous  portion  of  the  temporal 
bone  the  external  and  internal  borders  meet,  forming  two 
processes,  which  cross  each  other,  the  former  passing  inward  to 
the  posterior,  the  latter  forward  to  the  anterior,  clinoid  pro- 
cesses.    The  free  internal   border   is   concave,    and    bounds    a 


Fig.  142. — Meuiskctiun  of  Brain,  showing  Lmi'ortant  Sinuses. 
Falx  cerebri.  2,  2.  Its  convex  border,  with  the  great  longitudinal  sinus.  3.  Its  concave 
border.  4,  4.  Inferior  longitudinal  sinus.  5.  Base  of  falx  cerebri.  6.  Straight  sinus. 
7.  Apex  of  falx  cerebri.  8.  Right  half  of  the  tentorium,  seen  from  below.  9.  Right 
lateral  sinus.  10.  Superior  petrosal  sinus.  11.  Inferior  petrosal  sinus.  12.  Posterior 
occipital  sinus.  13.  Falx  cerebelli.  14.  Optic  nerve.  15.  Motor  oculi.  16.  Pathetic. 
17.  Trigeminus.  18.  Abducens.  19.  Facial  and  auditory  nerves.  20.  Glossophar}ngeal, 
pneumogastric,  and  spinal  accessory  nerves.  21.  Hypoglossal  nerve.  22.  First  cervical 
nerve.      23.   Second  cervical  nerve.      24,  24.   Upper  extremity  of  ligamentum  denticulatum. 


triangular  opening,  within  which  are  found  the  corpora  quadri- 
gemina  and  the  crura  cerebri. 

The  Falx  Cerebelli,  or  Processus  Falciformis  Minor. — 
This  somewhat  triangular-shaped  process  of  dura  mater  ex- 
tends downward,  between  the  cerebellar  hemispheres  in  the 
posterior  incised  cerebellar  notch,  from  the  middle  of  the  pos- 


THE   MEMBRANES   OF   THE    BRAIN.  283 

terior  border  of  the  tentorium  cerebelli,  to  which  it  is  attached. 
Its  posterior  margin  is  united  to  the  internal  occipital  crest,  and 
as  it  approaches  the  foramen  magnum  it  often  divides  into  two 
small  folds,  which  are  lost  on  the  sides  of  this  foramen. 

At  the  base  of  the  skull  the  dura  gives  off  a  shelf-like  process 
which  forms  a  roof  for  the  pituitary  fossa  and  has  a  central 
opening  through  which  passes  the  infundibulum.  This  process 
is  called  the  diaphragma  sellae. 

The  dura  mater  is  composed  of  white  fibrous  and  elastic 
tissue,  arranged  in  bundles,  which  cross  each  other  rather 
obliquely,  save  in  the  falx  and  tentorium,  where  they  have  a 
radial  arrangement.  The  inner  surface  of  the  dura  is  lined  with 
flattened  endothelium,  as  are  the  parts  of  the  outer  surface  not 
attached  to  the  bones.  The  dura  mater  is  traversed  by  a  system 
of  connective-tissue  spaces  which  are  located  between  the  bun- 
dles of  connective  tissue.  These  spaces  are  in  reality  lymphatic 
canals,  and  communicate  with  the  subdural  space.  Within  them 
exist  large,  flattened,  connective-tissue  cells.  They  can  be  in- 
jected by  inserting  a  cannula  directly  into  the  membrane,  when 
the  injected  material  will  escape  into  the  subdural  space.  This 
fact  is  very  important  from  a  surgical  point  of  view,  because  it 
readily  explains  how  micro-organisms  gain  entrance  through  the 
dura  and  infect  the  meninges,  producing  abscess  or  extensive 
leptomeningitis.  In  the  dura,  on  each  side  of  the  superior 
longitudinal  sinus,  exist  small  diverticuli,  or  venous  spaces 
(lacunae  venosse  laterales).  In  which  the  middle  meningeal  veins 
frequently  terminate ;  these  spaces  communicate  both  with  the 
diploic  veins  and  the  longitudinal  sinus. 

The  arteries  which  supply  the  dura  mater  are  derived  chiefly 
from  the  anterior,  middle,  and  posterior  meningeal.  These 
vessels  are  very  abundant,  and,  In  general,  course  between  the 
dura  and  the  internal  table  of  the  skull,  where  they  subdivide 
into  a  large  number  of  small  twigs,  which  penetrate  the 
Internal  table  of  the  skull,  conveying  nourishment  to  the  bones. 
These  so-called  meningeal  arteries  are  mainly  distributed  to 
the  bones  of  the  skull,  the  only  one  of  the  meninges  which  they 
supply  being  the  dura  mater,  hence  this  term  meningeal  is 
somewhat  misleading. 


284  CENTRAL  NERVOUS  SYSTEM. 

The  arteries  of  the  dura  mater  are  accompanied  by  veins 
whicli  receive  blood  from  the  dura  and  the  cranial  bones;  after 
anastomosing  with  the  diploic  veins  they  empty  into  the  various 
sinuses,  with  the  exception  of  the  veins  which  accompany  the 
middle  meningeal  arteries,  which  leave  the  skull  through  the 
foramen  spinosum  to  reach  the  internal  maxillary  vein. 

The  nerve  supply  of  the  dura  is  mainly  by  filaments  from  the 
fourth,  the  fifth,  and  twelfth  cranial  nerves,  and  from  the  sym- 
pathetic. 

THE  ARACHNOID  MEMBRANE. 

The  arachnoid  is  an  exceedingly  thin  membrane,  made  up  of 
delicate  bundles  of  fibrous  tissue,  and  is  covered  both  on  its  inner 
and  outer  surface  with  endothelium.  It  is  located  between  the 
pia  and  dura  mater,  being  separated  from  the  former  by  the 
subarachnoid  space  and  from  the  latter  by  the  subdural  space. 
This  membrane  passes  over  the  various  convolutions  and 
fissures  of  the  cerebrum  and  cerebellum  without  dipping  into 
the  fissures,  with  the  exception  of  those  that  contain  processes 
of  dura  mater.  It  also  forms  tubular  sheaths,  which  accompany 
the  nerve-fibers  through  their  foramina.  This  membrane  is 
easily  demonstrated  by  simply  injecting  air  beneath  it  by  means 
of  a  small  blow-pipe.  Between  the  arachnoid  and  the  pia  exists 
a  loose  connective  tissue,  the  subarachnoid  tissue,  which  consists 
of  numerous  fibrous  bands  or  trabeculae  lined  by  endothelium, 
which  pass  from  the  under  surface  of  the  arachnoid  to  the  pia 
mater,  the  meshes  between  the  trabeculae  forming  spaces  which 
differ  as  to  size  ;  these  spaces  in  the  subarachnoid  tissue  con- 
tain a  large  part  of  the  cerebrospinal  fluid,  and  are  called  sub- 
arachnoid spaces.  It  may  be  mentioned,  however,  that  over 
some  parts  of  the  convexity  and  sides  of  the  hemispheres 
the  subarachnoid  space  is  partially  or  completely  obliterated, 
owing  to  the  fusion  of  the  arachnoid  and  pia,  they  being  insepar- 
ably blended.  Over  the  posterior  two-thirds  of  the  base  there  is 
a  broad  separation  or  space  left  between  these  two  membranes, 
which  interval  forms  the  very  large  subarachnoid  space.  The 
arachnoid  has  but  a  limited  blood  supply,  and,  so  far  as  I  am 
aware,   no  nerve  supply,  although  nerve    filaments  have  been 


THE    MEMBRANES   OF   THE   BRAIN.  28s 


found  in  the  arachnoid  of  ruminants  by  Volkmann.  Bochdalek, 
and  Luschka.  These  come,  according  to  Bochdalek,  from  the 
motor  division  of  ^ the  trigeminus,  from  the  facial,  and  from  the 
spinal  accessory  nerves. 


SUBARACHNOID  SPACES. 

Over  the  convexity  of  the  cerebral  convolutions  only  a  slight 
separation  exists  between  the  arachnoid  and  the  pia  mater  ; 
hence  the  arachnoid  space  is  very  shallow  ;  but  over  the  base, 
especially  the  posterior  two-thirds,  a  wide  separation  exists 
between  these  two  membranes,  so  that  very  large  spaces  exist 
in  the  exceedingly  loose  meshwork  of  the  subarachnoid  tissue, 
which  contain  most  of  the  cerebrospinal  fluid.  These  spaces 
are  continuous  in  front  and  behind  with  the  subarachnoid 
spaces  of  the  spinal  cord.  Two  large  subarachnoid  spaces 
exist  at  the  base  of  the  brain  :  the  subarachnoid  space  of  the 
cerebellum  and  medulla  oblongata  (the  "  cisterna  magna  cere- 
bellomedullaris  ")  and  the  basal  subarachnoid  space. 

The  former,  the  space  of  the  cerebellum  and  medulla,  is 
situated  between  the  dorsal  surface  of  the  medulla  and  the 
inferior  surface  of  the  cerebellum.  It  is  separated  in  front  from 
the  cavity  of  the  fourth  ventricle  by  a  process  of  pia  mater, — the 
tela  choroidea  inferior, — which  forms  the  roof  of  the  lower  part 
of  this  ventricle  ;  above,  it  passes  over  the  inferior  surface  of  the 
vermis,  extending  laterally  over  the  amygdalar  lobes.  This 
space  is  continuous  below  with  the  posterior  arachnoid  space  of 
the  spinal  cord.  It  is  in  communication  with  the  cavity  of  the 
fourth  ventricle  by  an  opening  in  the  middle  of  the  tela  choroidea 
inferior,  called  the  foramen  of  Magendie.  Laterally,  this  space 
communicates  with  the  cavity  of  the  ventricle  by  two  openings  in 
the  pia  at  the  extremities  of  the  lateral  recesses,  which  are  called 
the  foramina  of  Key  and  Retzius. 

The  basal  subarachnoid  space  extends  in  front  of  the  medulla, 
pons,  interpeduncular  space,  and  crura  cerebri,  as  far  forward 
as  the  optic  chiasm,  and  laterally  to  the  margins  of  the  temporal 
lobes.  This  large  space  is  continuous  with  the  anterior  sub- 
arachnoid  space  of  the   cord,   and,  above,    communicates   with 


286 


CENTRAL  NERVOUS  SYSTEM. 


several  small  spaces — one  in  front  of  the  optic  chiasm,  one  in 
each  fossa  SyKii.  and  a  space  over  the  corpus  callosiim  ;  pos- 
teriorly, it  is  continuous  with  the  space  of  the  cerebellum  and 
medulla. 

The    cerebrospinal    tluid    which    occupies    the    subarachnoid 
space   is   continuous    with   that   within    the    cerebral    ventricles 


.,^^\ --^- 


>r^:. : 


Fig.  143. — Section  ok  the  Postekiok  and  Lower  Parts  of  the  Brain  Within  the 

SKUI.L  to  EXHIHIT  the  SlIiARACHNOII)  Sp.'VCE  AND  ItS   RELATION  TO  THE  VENTRICLES. 

— i^A/ter  Key  and  Ketziiis.)  [From  Quain.) 
I,  1' .  Atlas  vertebra.  2.  Odontoid  process  of  the  axis.  2',  3.  Third  ventricle.  4.  Fourth 
ventricle.  C.C.  Corpus  callosum.  C''.  Gyrus  fornicatus.  C.  Cerebellum.  /.Tentorium. 
/.  Pituitary  body.  c.i'.  Central  canal  of  the  cord.  /"M,  in  the  cerebellomedullary  part 
of  the  subarachnoid  space,  is  close  to  the  foramen  of  Magendie,  by  which  tliat  space  com- 
municates with  the  fourth  ventricle. 


through  openings  in  the  pia  mater  of  the  medulla  oblongata 
(foramina  of  Magendie,  Key,  and  Retzius).  It  is  also  continu- 
ous with  the  fluid  in  the  perineural  and  perivascular  spaces. 
The  cerebrospinal  fluid  forms  a  perfect  water-bed,  which  pro- 
tects and  supports  all  that  part  of  the  base  of  the  cerebrum, 
except  the  orbital  part  of  the  frontal  lobes  and  the  basal  surface 
of  the  apices  of  the  temporal  lobes,  which  rest  on  membranes 
covering  bone.  This  fluid  also  forms  a  bed  for  the  pons,  cere- 
bellum, and  medulla  (Fig.  143). 


THE   MEMBRANES   OF   THE   BRAIN. 


287 


THE  PACCHIONIAN  GLANDS,   OR  THE  ARACHNOID  VILLI. 

These  glandular-like  bodies  are  collections  of  whitish  granula- 
tions of  variable  size  which  begin  to  appear  about  the  seventh 
year  of  life,  and  continue  to  grow  as  age  advances.  They  are 
found  in  the  following  situations:  (i)  Along  the  superior  longi- 
tudinal sinus,  where  they  perforate  the  dura  and  become  lodged 
into  irregular  pits  or  depressions  in  the  calvarium  ;  (2)  pro- 
jecting from  the  inner  surface  of  the  dura  into  the  superior 
longitudinal  sinus  ;  (3)  along  the  margin  of  the  fissure  of 
Sylvius  ;  (4)  on  the  surface  of  the  pia  near  the  margin  of  the 
hemisphere. 


SUBARACHNOID  SPACE 


Superior  longitudinal  sinus 


PA CCHIONIA N  BODY 


CORPUS  CALLOSUM 


Fig.   144.. — Coronal  Section  Through  the   Great   Longitudinal   Fissure,  Showing 
THE  Meninges. — {Key  and  Retzius.) 


The  Pacchionian  bodies  are  not  glandular  in  structure. 
Luschka  has  shown  that  they  are  the  arachnoid  villi,  which  have 
enlarged  and  in  their  growth  have  passed  through  small  openings 
existing  in  the  inner  layer  of  the  dura,  which  openings  commu- 
nicate with  large  venous  spaces  in  that  membrane  on  each  side 
of  the  longitudinal  fissure.  In  their  growth  outward  they 
invaginate  the  outer  layer  of  the  dura,  and  by  pressure  cause 
the  absorption  of  bone  which  produces  the  irregular  pits  in  the 
calvarium  in  which  they  are  lodged. 

These    bodies  consist  of   a  spongy   network    of  connective 


288  CENTRAL  NERVOUS  SYSTEM. 

tissue,  similar  to  and  continuous  with  tlie  subarachnoid  tissue. 
They  are  covered  by  the  outer  layer  of  the  dura  and  the  arach- 
noid, and  may  serve  for  the  outflow  of  lymph  from  the  subdural 
and  subarachnoid  spaces  into  the  sinuses  of  the  dura  mater, 
especially  the  superior  longitudinal  sinus  (Fig.  144). 


THE   PIA  MATER. 

The  pia  mater  of  the  brain  is  a  very  vascular  membrane 
applied  to  the  entire  cortical  surface  of  the  cerebrum  and  cere- 
bellum, and  dips  down  into  their  various  fissures  and  sulci.  It 
sends  a  reduplication  or  fold  into  the  ventricles  of  the  brain, 
which  forms  the  velum  interpositum  and  choroid  plexuses. 
Great  numbers  of  small  vessels  which  penetrate  the  cortex  of 
the  brain  are  given  off  from  the  inner  surface  of  the  pia  mater. 
At  the  base  of  the  brain  the  pia  is  much  thickened,  and  invests 
the  crura  cerebri,  pons,  and  medulla,  and  gives  oft  to  the  central 
o-anglia  a  number  of  long  straight  vessels  which  perforate  the 
brain  substance,  forming  the  anterior  and  posterior  perforated 
spaces.  The  pia  mater  consists  of  rich  plexuses  of  blood-vessels, 
deriv^ed  from  the  internal  carotid  and  vertebral  arteries,  which 
are  supported  by  delicate  fibrous  connective  tissue,  which  tissue 
surrounds  the  blood-vessels  and  gives  off  tubular  prolongations 
to  the  vessels  which  pass  into  the  brain  substance,  forming  for 
them  loose  perivascular  sheaths,  the  spaces  of  which  are  con- 
tinuous with  the  subarachnoid  spaces. 

The  nerves  distributed  to  the  pia  accompany  the  blood-vessels 
and  are  derived  from  the  third,  fifth,  sixth,  facial,  glossopharyn- 
geal, pneumogastric,  spinal  accessory,  and  sympathetic. 


THE  VELUM  INTERPOSITUM  AND  CHOROID  PLEXUSES. 

The  velum  interpositum,  or  tela  choroidea  superior,  is  a  dupli- 
cature  or  fold  of  pia  mater,  triangular  in  shape,  which  has 
extended  into  the  ventricles  of  the  brain  after  passing  through 
the  transverse  fissure  of  Bichat.  This  fold,  the  velum  interposi- 
tum. consists  of  two  lamellae,  a  dorsal  and  a  ventral,  between 
which  exists  subarachnoid  tissue.     It  lies  beneath  the  fornix  and 


THE   MEMBRANES   OF    THE    BRAIN.  289 

splenium  of  the  corpus  callosum,  its  dorsal  lamella  being  united 
with  the  ventral  surface  of  these  bodies,  and  above  the  optic 
thalami  and  corpora  quadrigemina,  its  ventral  lamella  uniting 
with  the  optic  thalami. 

It  overlies  the  body  of  the  third  ventricle,  forming  for  it  a 
membranous  roof,  and  extends  over  each  optic  thalamus  as  far 
as  the  oblique  grooves  on  its  superior  surface.  The  posterior 
part  or  base  of  this  triangular  fold  of  pia  mater  is  continuous 
with  the  pia  mater  covering  the  inferior  surface  of  the  occipital 
lobes  and  the  superior  surface  of  the  cerebellum.  The  apex  of 
the  fold  is  bifid,  each  division  terminatino-  just  dorsal  to  the  ante- 


FiG.  145. — Vertical  Section  of  the  Cortex  Cerebri  and  Its  Membranes.  X  2^. 
— {After  Landois  and  Stirling.) 

CO.  Cortex  cerebri,  p.  Intima  pise  dipping  into  the  sulci,  a.  Arachnoid,  connected  with  / 
by  means  of  the  loose  subarachnoid  trabeculse  in  the  subarachnoid  space,  sa.  v,  v.  Blood- 
vessels,    d.   Dura.     sd.   Subdural  space. 


rior  pillar  of  the  fornix.  Its- lateral  margin  consists  of  a  convo- 
luted mass  of  highly  vascular  processes — the  choroid  plexuses 
of  the  lateral  ventricles.  These  processes  on  each  side  pass 
through  the  choroid  fissure  into  the  descending^  horn  of  the 
lateral  ventricles  to  their  extremities,  and  they  gradually  con- 
verge anteriorly,  and  between  the  foramina  of  Monro  they 
become  continuous  with  each  other.  From  this  junction  of  the 
choroid  plexuses  of  the  lateral  ventricles  two  small  plexuses 
pass  backward  along  the  middle  of  the  under  surface  of  the 
velum  interpositum,  and  descend  into  the  cavity  of  the  third 
ventricle  to  form  the  choroid  plexus  of  that  ventricle.  The 
19   . 


290 


CENTRAL  NERVOUS  SYSTEM. 


choroid  plexuses  of  both  the  hiteral  and  third  ventricles  are 
covered  by  the  ventricular  epithelium,  as  is  that  part  of  the 
velum  interposituni  which  covers  the  third  ventricle. 

The   choroid  plexus   is   made    up  of  small  processes  of  pia 


Fig.  146. — View  ok  the  Upper  Surface  of  the  Velum  Interpositum,  Choroid 
Plexuses,  and  Corpora  Striata. — {From  Sappey,  after  Vicqd'Azyr.) 

.  Fore-part  of  the  tela  choroidea  or  velum  interpositum.  2,  2.  Choroid  plexus.  3,  3.  Left 
vein  of  Galen  partly  covered  by  the  right.  4.  Anterior  pillars  of  the  fornix  divided  in 
front  of  the  foramen  of  Monro  ;  on  either  side  are  seen  small  veins  from  the  front  of  the 
corpus  callbsum  and  the  septum  lucidum.  5.  Vein  of  the  corpus  striatum.  6.  Convoluted 
marginal  vein  of  the  choroid  plexus.  7.  Vein  rising  from  the  thalamus  opticus  and  corpus 
striatum.  8.  Vein  proceeding  from  the  inferior  cornu  and  hippocampus  major.  9.  One 
from  the  posterior  cornu.  11.  Fornix  divided  near  its  middle  and  turned  backward. 
12.   Lyra.     13.   Posterior  pillar  of  the  fornix.      14.  The  splenium  of  the  corpus  callosum. 


mater,  which  consist  principally  of  the  ramifications  of  great 
numbers  of  small  blood-vessels  arranged  in  the  form  of  glom- 
eruli and  held  together  by  a  delicate  connective-tissue  stroma, 
producing  a  villous-like  appearance.     These  processes  are  cov- 


THE    MEMBRANES    OF   THE    BRAIN.  291 

ered  by  cubic  epithelial  cells,  which  in  the  new- born  are  ciliated; 
they  usually  contain  a  yellowish  pigment  or  minute  droplets  of 
fat.  The  choroid  plexuses  are  supplied  by  the  anterior  and  poste- 
rior choroid  arteries.  The  choroid  veins  return  the  blood  from 
these  plexuses,  and  at  the  foramen  of  Monro  join  the  veins  of 
the  corpora  striati,  to  form  the  veins  of  Galen  (Fig.  146). 


THE    TELA    CHOROIDEA    INFERIOR   AND  CHOROID    PLEXUSES 
OF  THE  FOURTH  VENTRICLE. 

The  tela  choroidea  inferior  is  a  process  of  pia  mater  analogous 
to  the  velum  interpositum.  It  consists  of  two  lamellae  separated 
by  subarachnoid  tissue,  within  which  courses  the  posterior  infe- 
rior cerebellar  artery.  The  ventral  lamella  is  prolonged  from 
the  medulla  oblongata,  and  overlies  the  lower  half  of  the  fourth 
ventricle,  forming,  with  the  inferior  medullary  velum,  a  roof  for 
that  part  of  this  ventricle.  This  portion  of  the  ventral  lamella 
is  somewhat  triangular  in  shape,  its  base  being  reflected  over 
the  inferior  margin  of  the  velum  medullare  inferioris,  and  its 
apex  extending  just  below  the  obex.  The  dorsal  lamella  is 
reflected  upon  the  inferior  vermis  and  the  amygdala  of  the  cere- 
bellum, where  it  becomes  continuous  with  the  pia  mater.  Both 
lamellae  are  covered  by  epithelium. 


CHOROID  PLEXUSES  OF  THE  FOURTH  VENTRICLE. 

From  the  inferior  surface  of  the  ventral  lamella  projects  a 
series  of  small,  vascular,  villous  tufts,  covered  by  the  epithelium 
lining  the  roof  of  the  ventricle  ;  these  are  the  choroid  plexuses 
of  the  fourth  ventricle.  They  consist  of  a  middle  and  a  lateral 
set  for  each  side,  which  are  continuous  with  each  other  in  front, 
and  are  called  the  middle  and  lateral  choroid  plexuses.  The 
middle  set  is  located  on  each  side  of  the  middle  line  of  the 
ventral  or  inferior  lamella,  extending  from  the  foramen  of 
Magendie  forward  to  the  margin  of  the  inferior  medullary  velum, 
over  which  margin  the  ventral  lamella  is  reflected.      Here  the 


292  CENTRAL  NKRVoUS  SYSTEM. 

two  sets  unite  in  the  form  of  a  letter  T.  the  vertical  part  cor- 
responding to  the  middle  sets,  while  the  horizontal  part  cor- 
responds to  the  lateral  sets.  The  lateral  set  of  each  side 
continues  alone  the  margin  of  the  inferior  medullary  velum  into 
the  lateral  recesses  of  the  ventricle,  terminating  at  the  lateral, 
openings  in  the  pia  mater. 


CHAPTER  VIII. 

FORE-BRAIN  OR  PROSENCEPHALON. 

The  cerebrum  is  the  largest  part  of  the  encephalon.  It  rests 
in  front,  in  the  anterior  and  middle  fossa  of  the  skull.  It  is 
supported  behind  by  the  tentorium  cerebelli,  which  serves  to 
separate  it  from  the  cerebellum.  In  man  it  forms  about  three- 
fifths  of  the  entire  encephalon.  Its  upper  surface  is  ovoid  and 
convex,  narrow  in  front  and  broad  behind.  Its  anteroposterior 
diameter  is  about  eighteen  cm.  (seven  inches),  and  its  great- 
est transverse  diameter,  which  corresponds  to  the  parietal 
protuberances,  is  about  thirteen  cm.  (five  inches).  Its  under 
surface  is  somewhat  irregular.  In  front  the  frontal  lobe  is  seen 
resting  in  the  anterior  fossa,  the  temporal  lobe  occupying  the 
middle  fossa,  and  the  occipital  lobe  resting  upon  the  tentorium 
cerebelli.  The  cerebrum  is  divided  into  two  hemispheres,  right 
and  left,  by  a  deep  cleft  the  longitudinal  fissure.  This  great 
fissure  extends  to  the  base  of  the  brain  in  front  and  behind,  but 
is  bridged  at  its  middle  by  a  broad  band  of  fibers  running 
transversely, — the  corpus  callosum,  which  is  the  great  commis- 
sure of  the  cerebrum.  This  commissure  forms  a  sort  of  floor 
for  the  superior  division  of  this  fissure,  and  lodges  a  long  pro- 
cess of  dura  mater — the  falx  cerebri.  Each  hemisphere  is  con- 
vex on  its  outer  surface,  to  rest  against  the  concavit)^  of  the 
cranial  vault.  It  is  narrowed  anteriorly,  broadened  posteriorly, 
and  presents  a  flattened  median  surface,  which  forms  the  outer 
boundary  or  side  of  the  great  longitudinal  fissure.  The  cere- 
brum is  composed  of  both  gray  and  white  matter,  the  former 
entirely  surrounding  the  latter.  The  surface  of  the  gray  invest- 
ing matter  presents  various  infoldings  or  depressions  and  ele- 
vations of  different  size.     The  elevations  bear  the  name  of  gyri 

or    convolutions ;  the   depressions,   of    fissures    or    sulci.     The 

293 


294  CENTRAL  NERVOUS  SYSTEM. 

effect  ot  the  hssures  and  convolutions  is  to  increase  enormously 
the  surface  extent  of  gray  matter, — the  extent  of  surface  in  the 
fissures  being  double  that  of  the  convexity  of  the  gyri, — upon 
the  amount  of  which  gray  matter  the  higher  intellectual  attri- 
butes depend.  As  we  descend  in  the  scale  of  animal  life,  the 
convolutions  become  more  simple  and  flattened,  the  fissures 
less  deep  and  the  cerebrum  is  greatly  reduced  in  size. 


FISSURES. 

The  fissures  serve  to  divide  the  cerebrum  into  its  lobes,  and 
form  its  important  anatomic  landmarks.  They  are  divided  into 
the  primary  or  interlobar  fissures,  and  the  secondary  or  intralobar 
fissures.  The  former  are  of  great  depth  (twenty-five  mm. — 
almost  an  inch ;  exceptionally,  an  inch  or  more),  are  constant,  and, 
with  slight  variation  have  a  uniform  size,  location,  and  direction. 
They  are  as  follows :  The  great  longitudinal  fissure,  subdivided 
into  a  superior  and  an  inferior  portion  ;  the  transverse  or  fissure 
of  Bichat;  the  fissure  of  Sylvius;  the  fissure  of  Rolando;  the 
parieto-occipital  ;  the  inter-  or  intraparietal  ;  the  callosomargi- 
nal  ;  the  calcarine  ;   and  the  collateral. 

The  secondary  fissures — often  called  sulci  for  the  sake  of  dis- 
tinction— are  short  and  shallow,  and  do  not  present  the  typical 
marks  as  given  above.  They  are  numerous  and  complicated, 
and  present  many  variations.  The  important  ones  will  be  men- 
tioned in  describine  the  lobes. 


THE  FISSURES  OF  THE  EXTERNAL  SURFACE  OF  EACH 
HEMISPHERE. 

The  longitudinal  fissure  separates  the  cerebrum  into  its 
hemispheres,  completely  dividing  the  anterior  portion  of  the 
frontal  lobe  and  the  entire  occipital  lobe,  the  middle  portion  of 
the  fissure  being  interrupted  by  the  bridge  of  cross  fibers — the 
corpus  callosum. 

The  transverse  fissure,  in  form  like  the  letter  U,  separates 
the  cerebrum  above  from  the  cerebellum  below.  This  fissure  is 
continuous    on    each    side    with    the    choroid    fissure,    which  is 


A.M.F 


Fig.  147. — Photograph  of  the  Superior  Surface  of  the  Cerebrum. 
A.M.F.  Anterior  median  fissure  (longitudinal).  Mar.  Gyr.  Marginal  gyrus.  S.F.G.  Superior 
frontal  gyrus.  S.F.Fis.  Superior  frontal  fissure.  M.F.G.  Middle  frontal  gyrus.  Pre. 
Sul.  Precentral  sulcus.  I.F.Fis.  Inferior  frontal  fissure.  Asc.F.G.  Ascending  frontal 
gyrus.  Intra.  P.Fis.  Intraparietal  fissure.  Supra.  M.G.  Supramarginal  gyrus.  S.P.C. 
Superior  parietal  convolution.  Ang.  G.  Angular  gyrus.  M.O.G.  Middle  occipital 
gyrus.  I.O.G.  Inferior  occipital  gyrus.  S.O.G.  Superior  occipital  gyrus.  Ext.  P.O.F. 
Externa]  parieto-occipital  fissure.  R.  Cerebellar  H.  Right  cerebellar  hemisphere.  S. 
Vermis.  Superior  vermis.  P.I.N.  Posterior  incised  cerebellar  notch.  L.  Cerebellar  H. 
Left  cerebellar  hemisphere.  I.  E.G.   Inferior  frontal  gyrus. 

29s 


FORE-BRAIN  OR  PROSENCEPHALON. 


297 


really  a  prolongation  of  the  transverse  fissure.  The  choroid 
fissure  is  due  to  an  infolding  of  the  median  surface  of  the 
h-emisphere  wall,  producing  an  arch-like  groove  between  the 
fornix    and  the    optic    thalamus.     It   is   closed  by  an  invagina- 


FiG.  148. — Photograph  of  the  External  Surface  of  the  Brain. 
I.F.S.  Inferior  frontal  sulcus  or  fissure.  I. E.G.  Inferior  frontal  gyrus.  M.F.G.  Middle 
frontal  gyrus.  S.F.S.  Superior  frontal  sulcus.  S.F.G.  Superior  frontal  gyrus.  Pr.S. 
Precentral  sulcus.  Acs.F.  Ascending  frontal  gyrus.  R.F.  Rolandic  fissure.  Asc.P. 
Ascending  parietal  convolution.  Intra. P.F.  Intraparietal  fissure.  S.P.G.  Superior  parie- 
tal gyrus.  Intra.P.F.H.  (Horizontal  limb)  Intraparietal  fis.sure.  S.M.G.  Supramar- 
ginal  gyrus.  Ang.G.  Angulargyrus.  E.P.O.  External  parieto-occipital  fissure.  S.O.S. 
Superior  occipital  sulcus.  S.O.C.  Superior  occipital  convolution.  M.O.C.  Middle  occi- 
pital convolution.  I.O.S.  Inferior  occipital  sulcus.  I.O.C.  Inferior  occipital  convolution. 
I.T.C.  Inferior  temporal  convolution.  M.T.S.  Middle  temporal  sulcus.  Par.F.  Parallel 
fissure.  C.  Cerebellum.  M.T.S.  Middle  temporal  sulcus.  M.T.C.  Middle  temporal 
convolution.  I.T.C.  Inferior  temporal  convolution.  S.T.C.  Superior  temporal  convolu- 
tion. T.P.G.  Temporoparietal  annectant  gyri.  T.T.G.  Transverse  temporal  gyrus. 
P.L.S.  Posterior  limiting  sulcus.  G.L.I.  Gyrus  longus  insulse.  G.B.I.  Gyrus  brevis 
insulge.   S.C.I.   Sulcus  centralis  insulse. 

tion  of  a  process  of  pia  mater  (the  choroid  plexus)  covered 
with  ventricular  epithelium.  In  order  to  expose  this  fissure, 
this  process  of  pia  mater  must  be  rather  forcibly  removed, 
when  a  curved  fissure  will  be  seen  on  each  side,  extending  from 


298  CENTRAL  NERVOUS  SVSTKM. 

the  beeinnine  of  the  descendino-  horn  of  the  lateral  ventricle  to 
the  corresponding  foramen  of  Monro.  These  fissures  together 
form  the  great  transverse  fissure,  which  emerges  between  the 
corpora  quadrigemina  and  the  inferior  surface  of  the  occipital 
lobes  above  and  the  superior  surface  of  the  cerebellum  below. 

The  fissure  of  Sylvius  is  the  largest  of  the  primary  fissures, 
and  the  first  one  to  be  developed,  appearing  at  about  the  third 
month  of  fetal  life.  It  is  in  reality  not  a  mere  cleft,  as  are 
most  of  the  other  external  fissures,  but  it  is  formed  by  the 
folding  together  of  the  hemisphere  into  an  arch,  the  concavity 
being  downward  near  the  brain-stem.  The  wide  space  thus 
formed  is  termed  the  fossa  or  vallecula  Sylvii.  This  fossa 
may  be  recognized  in  the  human  embryo  as  early  as  the  fifth 
week.  At  the  sixth  fetal  month  this  fossa  diminishes  in  size 
and  takes  on  a  triangular  form.  This  is  due  to  the  rapid 
growth  of  the  frontal,  parietal,  and  temporal  lobes,  their  margins 
coming  in  contact  with  one  another  and  overlapping  the  fossa 
to  form  opercula,  or  lids.  The  island  of  Reil  is  developed  from 
the  bottom  of  the  original  fossa,  and  is  covered  by  the  above- 
mentioned  opercula,  thus  narrowing  the  fossa  into  the  fissure  of 
Sylvius.  This  fissure  starts  at  the  base  of  the  brain,  a  little 
lateral  to  the  anterior  perforated  space.*  It  passes  outward 
and  forward  and  reaches  the  external  surface  of  the  cerebrum, 
where  it  turns  upward  and  backward,  dividing  into  two  limbs  :  a 
short  anterior  limb,  which  passes  vertically  upward  into  the  lower 
frontal  convolution,  where  it  ends  ;  and  a  long  or  horizontal  limb, 
which  passes  backward  and  gradually  upward  to  end  in  the 
division  of  the  parietal  lobe,  called  the  supramarginal  gyrus. 
It  is  common  for  this  fissure  to  bifurcate  at  its  termination. 
Deep  in  this  fissure,  hidden  by  the  overlapping  of  the  lower 
frontal  and  parietal  lobes  and  the  point  of  the  temporal  lobe, 
are  a  few  small  convolutions  or  gyri.  called  the  island  of  Reil. 
This  overlapping  of  the  lobules  is  called  the  operculum,  or  cover. 
The  Sylvian  fissure  separates  the  frontal  and  parietal  lobes 
above  from  the  temporal  below. 


*  The  anterior  limb  of  the  Sylvian  fissure  often  gives  oft  a  short  horizontal  branch,  which 
passes  into  the  lower  frontal  gyrus,  where  it  terminates. 


FORE-BRAIN  OR  PROSENCEPHALON.  299 

The  fissure  of  Rolando,  or  central  fissure,  is  one  of  the 
most  important  anatomic  landmarks  on  the  external  surface  of 
the  hemisphere.  It  is  always  present  in  man  and  the  higher 
mammalia,  develops  toward  the  close  of  the  fifth  month  of  fetal 
life,  and  appears  as  two  distinct  primitive  grooves,  separated  by 
a  slightly  elevated  portion,  which  later  becomes  hollowed  out, 
thus  bringing  about  the  junction  of  the  two  primitive  fissures  to 
form  the  fissure  of  Rolando.  The  Rolandic  fissure  is  of  ereat 
depth, — often  an  inch  or  more, — and  is  located  near  the  middle 
of  the  hemisphere.  It  usually  starts  as  a  distinct  notch  on  the 
median  surface  of  the  hemisphere  in  the  paracentral  lobule. 
Thence  it  takes  an  oblique  course  downward  and  slightly  for- 
ward, and  most  often  terminates  just  above  and  close  to  the 
horizontal  limb  of  the  Sylvian  fissure  ;  occasionally,  however,  it 
communicates  with  the  latter  fissure.  The  slope  of  this  fissure 
makes  an  angle  of  about  sixty-seven  degrees  with  the  superior 
margin  of  the  hemisphere.  It  lies  between  two  important  con- 
volutions, which  have  an  ascending  direction, — hence  their  name, 
ascending  gyri, — and  forms  the  boundary  between  the  frontal 
lobe  in  front  and  the  parietal  lobe  behind.  The  anterior 
ascending  gyrus,  which  forms  the  anterior  boundary  of  this 
fissure,  is  called  the  ascending  frontal  gyrus  ;  the  posterior  one, 
the  ascending  parietal  gyrus.  These  two  gyri  together,  be- 
cause of  their  position  midway  between  the  frontal  and 
parietal  lobes,  have  received  the  name  of  the  central  gyri  or 
convolutions. 

Theparieto-occipital  fissure  (occipital  of  Wilder),  developed 
at  the  fourth  fetal  month,  is  best  marked  on  the  median  surface 
of  the  hemisphere  ;  it  is,  however,  seen  on  the  outer  surface  as 
a  deep  and  oftentimes  wide  notch,  which  separates  the  parietal 
lobe  in  front  and  the  occipital  behind.  The  external  or  outer 
portion  of  this  cleft,  which  is  called  the  external  parieto-occipital 
fissure,  forms  an  anatomic  landmark  second  only  in  importance 
to  the  fissure  of  Rolando,  The  main  portion  of  this  fissure  is 
to  be  found  on  the  median  surface  of  the  hemisphere,  where  it 
is  seen  as  a  deep  cleft  passing  obliquely  downward  and  forward 
to  unite  with  a  fissure — the  calcarine — soon  to  be  described.  This 
union  produces  a  large  Y-shaped  junction,  which  incloses  a  very 


300  CENTRAL  NKRVOUS  SYSTEM. 

important  little  wedge-shaped  gyrus,  the  cuneus,  which  is  the 
half-vision  center. 

The  intra-  or  interparietal  fissure  serves  to  separate  the 
parietal  lobes  into  a  superior  and  an  inferior  division.  It  develops 
at  the  sixth  month  of  fetal  life  as  two  distinct  sulci,  one  parallel 
to  the  fissure  of  Rolando,  the  other  havingf  a  longritudinal  course 
close  to  the  margin  of  the  hemisphere  ;  they  unite  at  the  eighth 
or  ninth  month,  producing  a  continuous  fissure.  This  fissure 
starts  near  the  horizontal  limb  of  the  Sylvian  fissure,  runs  verti- 
cally upward,  parallel  to  the  Rolandic  fissure,  giving  off  a  slight 
vertical  sulcus,  which  continues  upward.  This  is  the  so-called 
postcentral  sulcus.  The  intraparietal  fissure  then  makes  an 
abrupt  curve  upward  and  backward,  to  terminate  beyond  the 
external  parieto-occipital  fissure.  It  is  separated  from  the  latter 
fissure  by  the  superior  occipital  gyrus,  and  often  joins  the  ante- 
rior occipital  fissure.  On  its  vertical  course  it  forms  the  posterior 
boundary  of  the  ascending  parietal  gyrus,  and  gives  off  the  above- 
mentioned  ascending  branch  just  before  it  passes  backward, 
called  the  postcentral  sulcus.  This  fissure  occasionally  extends 
into  the  Sylvian. 

The  calcarine  fissure,  which  unites  with  the  median  branch 
of  the  parieto-occipital  fissure,  branches  in  a  T-shape  from  the 
posterior  extremity  of  the  occipital  lobe,  which  is  its  point  of 
origin.  From  this  point  it  extends  forward  on  the  median  sur- 
face, and  unites  with  the  parieto-occipital  fissure,  making  with 
that  fissure  an  acute  angle,  then  passing  forward  and  slightly 
downward,  to  terminate  near  the  middle  of  the  median  surface 
of  the  temporal  lobe.  Its  anterior  portion,  which  is  a  deep 
cleft,  produces  in  the  posterior  horn  of  the  lateral  ventricle  a 
prominence  known  as  the  hippocampus  minor,  or  calcar  avis. 

The  collateral  fissure  is  seen  on  the  median  surface  of 
the  temporal  lobe  ;  it  is  below  the  calcarine  and  runs  parallel 
with  it.  It  passes  forward  to  near  the  commencement  of  the 
Sylvian  fissure  and  ends  in  the  tip  of  the  temporal  lobe.  Be- 
tween this  fissure  and  the  calcarine  exists  the  lingual  or  middle 
occipitotemporal  gyrus.  The  middle  portion  of  this  fissure  pro- 
duces a  projection  in  the  lateral  ventricle  called  the  eminentia 
collate  ralis. 


Fig.  149. — Photograph  of  the  Median  Surface  of  the  Brain. 

M.G.  Marginal  gyrus.  C.M.F.  Callosomarginal  fissure.  Forn.G.  Gyrus  fornicatus.  Para. 
S.  Paracentral  sulcus.  Para.  Paracentral  lobule.  R.F.  Rolandic  fissure.  Quad.L. 
Quadrate  lobe.  I.P.O.F.  Internal  parieto-occipital  fissure.  C.  Cuneus.  C.A.F.  Ante- 
rior calcarine  fissure.  L.L.  Lingual  lobule  or  gyrus.  Col.F.  Collateral  fissure.  C.P.F. 
Posterior  calcarine  fissure.  I.T.G.  Inferior  temporal  gyrus.  S. C.C.  Splenium  corpus 
callosum.  For.  Fornix.  C.C.  Corpus  callosum.  R.C.C.  Rostrum  of  corpus  callosum. 
G.C.C.    Genu  of  corpus  callosum. 


Fig.    150. — Vertical  Section  Through  Frontal  Lobe. 


FORE-BRAIN  OR  PROSENCEPHALON.  303 

The  callosomarginal  is  a  very  long  and  somewhat  tortu- 
ous fissure,  located  on  the  median  surface  of  the  hemisphere, 
and  becomes  developed  at  about  the  middle  of  the  fifth  month 
of  fetal  life.  It  begins  in  front,  below  the  rostrum  of  the  corpus 
callosum,  near  the  anterior  perforated  space,  passes  upward, 
outward,  and  forward,  pursuing  a  course  parallel  to  the  corpus 
callosum,  then,  turning  backward,  ends  near  the  margin  of 
the  hemisphere,  a  little  back  of  the  fissure  of  Rolando.*  It 
separates  the  marginal  convolution  above  from  the  gyrus  forni- 
catus  below,  and  forms  the  anterior  boundary  of  the  quadrate 
lobe  (Figs.  147,  148,  and  149). 


THE  CONVOLUTIONS,  GYRI,  OR  LOBULES. 

The  fissures — the  Sylvian,  Rolandic,  and  external  parieto- 
occipital— are  the  great  anatomic  landmarks  which  serve  to 
separate  the  external  surface  of  the  cerebral  hemisphere  into 
five  lobes — viz.,  the  frontal,  parietal,  temporosphenoid,  occipi- 
tal, and  the  central  lobe,  or  island  of  Reil. 


THE  FRONTAL  LOBE. 

The  frontal  lobe  in  man  constitutes  about  one-third  of  the 
whole  cerebral  hemisphere.  It  presents  on  transverse  section 
the  outline  of  a  spheric  triangle.  That  portion  which  rests  on 
the  orbital  plate  of  the  frontal  bone  is  termed  the  orbital  lobe. 
The  entire  frontal  lobe  is  bounded  posteriorly  by  the  fissure  of 
RolandOj  which  separates  it  from  the  parietal  lobe.  Its  inferior 
boundary  is  the  Sylvian  fissure.  Above,  it  forms  part  of  the 
margin  of  the  longitudinal  fissure.  Its  external  surface,  which 
is  convex,  presents  several  convolutions  or  gyri,  separated  by 
sulci  or  secondary  fissures.  The  three  following  gyri  have  a 
general  direction  from  before  upward  and  backward  :  ^\iQ.  first 
or  superior  fro7ital gyrus,  the  longest  of  the  three,  runs  parallel 
with  the  margin  of  the  hemisphere  of  which  it  is  a  part,  and  is 


*  In  many  brains  a  fissure  is  prolonged  backward  from  the  main  one  through   the   quadrate 
obe,  terminating  near  the  internal  parieto-occipital  fissure. 


304  CENTRAL  NERVOUS  SYSTEM. 

continuous  with  the  marginal  gyrus  on  the  median  surface,  the 
latter  being  only  the  mesial  surface  of  the  first  frontal  gyrus. 
In  front  it  reaches  the  apex  of  the  frontal  lobe  ;  behind,  it  is 
often  continuous  with  the  ascending  frontal  gyrus,  or  it  may  be 
separated  from  the  latter  by  the  superior  portion  of  the  pre- 
central  sulcus.  From  the  gyrus  below  it  is  separated  by  the 
superior  frontal  sulcus,  a  long,  shallow  fissure,  running  forward 
and  downward.  The  middle  or  second  frontal  gyi'us  is  much 
shorter  but  broader  than  its  fellow  above,  runs  from  below  up- 
ward and  backward,  and  at  its  upper  part  is  often  made  con- 
tinuous with  the  ascending  frontal  convolution  by  a  small  annec- 
tant  gyrus.  The  iiiferior  part  of  the  dorsal  portion  of  this 
lobule  is  prevented  from  coming  into  contact  with  the  ascending 
frontal  by  a  vertical  sulcus,  which  arises  just  above  the  fissure 
of  Sylvius  and  runs  parallel  to  the  fissure  of  Rolando.  This  is 
xh^  prece7itral  sulcus  above  referred  to.  It  is  deeper  than  most 
of  the  sulci,  and  sometimes  becomes  continuous  with  the  calloso- 
marginal  fissure  (Schwalbe).  It  forms  the  anterior  boundary  of 
the  ascending  frontal  or  central  gyrus,  separating  it  from  the 
second  and  third  frontal  gyri.  This  sulcus  often  presents  an 
anterior  limb,  wdiich  is  continuous  w^ith  the  inferior  frontal  fissure. 
The  main  sulcus,  usually  continuous,  is,  however,  often  sepa- 
rated into  two  or  three  divisions  by  small  annectant  gyri,  which 
serve  to  connect  the  frontal  gyri  with  the  anterior  central  or 
ascending  frontal  gyrus.  In  the  posterior  part  of  the  middle 
frontal  gyrus  of  the  left  side  exists  the  center  in  which  are 
stored  the  muscular  memories  used  in  writing  ;  hence,  when 
destroyed  agraphia  occurs.  The  third  or  inferior  frontal 
gyms  is  the  smallest  of  the  three.  It  passes  from  the  inferior 
portion  of  the  ascending  frontal  anteriorly  to  the  end  of  the 
frontal  lobe.  It  forms  the  anterior  operculum,  which,  together 
with  the  superior  and  inferior  opercula,  forms  a  roof  for  the  island 
of  Reil.  It  curves  around  both  limbs  of  the  Sylvian  fissure,  which 
produces  indentations  on  the  gyrus,  and  thus  divides  it  into 
three  parts.  According  to  Broca,  this  g>'rus  is  more  developed 
in  man  on  the  left  side,  because  of  the  fact  that  in  its  posterior 
area  exists  the  motor  speech  center.  It  is  separated  from  the 
second  frontal  gyrus  by  the  inferior  frontal  sulcus,  which  starts 


FORE-BRAIN  OR  PROSENCEPHALON. 


305 


from  about  the  middle  of  the  precentral  sulcus  and  passes  for- 
ward to  the  frontal  lobe,  M^here  it  bifurcates.  It  is  continuous 
below  with  the  orbital  lobe. 

A  very  important  part  of  the  frontal  lobe  lies  between  the 
precentral  fissure  and  the  fissure  of  Rolando.  This  is  the 
before-mentioned  ascending  frontal  gyrus,  also  called  the  anterior 
central  convolution.  It  begins  below  at  the  Sylvian  fissure,  where 
it  is  connected  with  the  ascending  parietal  gyrus,  passes  upward, 
and  unites  on  the  median  surface  of  the  hemisphere  with  the 
ascending  parietal  gyrus,  the  junction  being  termed  the  paracen- 
tral lobule.     Below,  this  convolution  forms  part  of  the  superior 


First  occipital  conv. 
Second  occipital  conv. 


Third  occipital  conv. 


'■a/  Co. 


•"v 


Fig.  151. — Diagrammatic  Representation  of  the  Lobes  of  the  Cerebrum. 


boundary  of  the  fissure  of  Sylvius.  It  is  connected  with  the 
three  frontal  lobules  by  small  annectant  gyri.  That  part  of  the 
frontal  lobe  anterior  to  the  ascending  frontal  or  anterior  cen- 
tral gyrus  is  often  called  the  prefrontal  region  or  lobe. 

The  inferior  surface  of  the  frontal  lobe,  which  rests  upon 
the  orbital  plate  of  the  frontal  bone,  is  termed  the  orbital 
lobe.  It  is  slightly  concave,  and  has  the  form  of  a  triangle,  the 
base  being  directed  anteriorly,  the  narrow  portion  or  apex 
pointing  posteriorly.  It  has  near  its  median  surface  a  well- 
marked  sulcus  or  groove,  which  forms  the  lateral  boundary  of 
the  basal  portion  of  the  superior  frontal  gyrus,  or,  as  it  is  called 


3o6  CENTRAL  NERVOUS  SYSTEM. 

here,  from  its  straight  course,  the  gyrus  rectus.  In  this  groove 
rests  the  oHactory  bulb  and  tract,  and  lience  it  is  also  called 
the  olfactory  sulcus.  The  margin  of  the  lobe  forms  part  of  the 
maro-inal  o-vrus  of  the  median  surface.  The  orbital  lobe  is 
subdivided  by  the  orbital  or  triradiate  sulcus  into  three  gyri. 
This  sulcus  is  irregularly  H-shaped,  and  might  almost  be  called 
compound,  being  made  up  of  a  number  of  smaller  sulci.  Its 
posterior  part  curves  laterally  around  from  the  Sylvian  fissure, 
to  end  near  the  root  of  the  olfactory  tract.  Three  or  four 
sulci,  running  from  before  backward,  communicate  with  this 
branch.  The  divisions  of  the  orbital  lobe  are  the  internal, 
anterior,  and  posterior  gyri,  which  are  the  basal  pordons  re- 
spectively of  the  superior,  middle,  and  inferior  frontal  convolu- 
tions (Fig.  157). 

THE  PARIETAL  LOBE. 

This  lobe  occupies  a  large  extent  of  a  cerebral  hemisphere. 
Its  upper  and  outer  surface  is  convex  ;  its  median  surface  is  flat, 
forming  part  of  the  boundary  of  the  superior  longitudinal  fissure, 
and  is  termed  the  quadrate  lobe.  The  parietal  lobe  is  located 
dorsal  to  the  frontal,  above  the  temporal,  and  ventral  to  the 
occipital  lobes.  Its  anterior  boundary  is  the  fissure  of  Rolando, 
which  separates  it  from  the  frontal  lobe  ;  its  posterior  boundary 
is  the  external  parieto-occipital  fissure,  wdiich  is  between  it  and 
the  occipital  lobe.  Its  lower  boundary  is  the  horizontal  limb  of 
the  Sylvian  fissure,  which  separates  it  from  the  temporosphenoid 
lobe.  The  intraparietal  fissure  separates  this  lobe  into  three 
convoludons — the  ascending  parietal  and  the  superior  and  infe- 
rior parietal. 

The  ascending  parietal  or  posterior  central  gyrus  is 
between  the  fissure  of  Rolando  in  front  and  the  ascending  or 
vertical  division  of  the  intraparietal  fissure  behind.  It  ascends 
to  the  median  surface,  where  it  is  continuous  with  the  ascending 
frontal,  the  union  of  the  two  forming  the  paracentral  lobule.  It 
is  separated  from  the  superior  parietal  lobule  by  the  postcentral 
sulcus,  which  is  only  a  condnuation  or  a  branch  of  the  intra- 
parietal fissure.  Below,  it  is  also  continuous  with  the  ascending 
frontal  or  anterior  central  gyrus.     This  g)Tus,  with  its  fellow  of 


FORE-BRAIN  OR  PROSENCEPHALON. 


307 


the  frontal  lobe,  forms  two  very  important  gyri,  which,  from  their 
central  position,  are  termed  the  central  convolutions  (anterior 
and  posterior),  and  from  their  important  relation  to  the  great 
motor  tract  they  are  termed  the  motor  convolutions.  From 
this  extensive  area  the  fibers  arise  which  form  the  motor  tract, 


Fig.  152. — -Trontal  Section  through  Parietal,  Temporal,  and  Occipital  Lobes, 
Together  with  the  Cerebellum. 
P.  O.  F.    Parieto- occipital    fissure.     P.  L.    Parietal    lobe.      S.  T.  G.    Superior    temporal    g>'rus. 
C.    Cuneus.      C.  F.  Calcarine  fissure.      T.  T.  G.   Middle  temporal  gyrus.      L.  L.    Lingual 
lobule.       I.  T.  G.    Inferior  temporal    gyrus.       C.  D.    Corpus  dentatum.      T.   Tonsil.      N. 
Nodule. 


and  into  this  and  the  adjacent  parietal  area  pass  the  fibers  of  the 
sensory  tracts. 

The  superior  parietal  convolution   or  lobule   lies  above 
the   horizontal   division  of  the    intraparietal    fissure,  along   the 


3o8  CENTRAL  NERVOUS  SYSTEM. 

margin  of  the  hemisphere.  It  is  dorsal  to  the  upper  part  of  the 
ascending  parietal  gyrus,  being  separated  from  it  by  the  post- 
central sulcus.  It  extends  backward  to  the  occipital  lobe,  the 
dividing-line  being  the  external  parieto-occipital  fissure. 

The  inferior  parietal  convolution  is  below  the  superior, 
being  separated  from  it  by  the  intraparietal  fissure.  It  is  con- 
tinuous behind  with  the  occipital  lobe  and  in  front  with  the  lower 
part  of  the  ascending  parietal.  Below,  it  is  separated  from  the 
temporal  lobe  by  the  horizontal  limb  of  the  Sylvian  fissure.  It 
is  made  up  of  the  supramarginal,  angular,  and  postparietal 
convolutions,  their  principal  direction  being  downward  and 
arching  around  the  end  of  the  Sylvian  and  first  temporal  fis- 
sures. The  siipraniai'ginal  gyrus  lies  below  and  posterior  to 
the  intraparietal  fissure,  and  between  the  inferior  part  of  the 
ascending  parietal  lobule  and  the  upper  end  of  the  horizontal 
limb  of  the  Sylvian  fissure,  which  it  encircles.  It  is  continuous 
behind  with  the  angular  and  below  with  the  first  temporo- 
sphenoid  gyri.  The  angular  gyriis  is  just  back  of  the  supra- 
marginal,  with  which  it  is  continuous.  Above,  it  is  bounded  by 
the  intraparietal  fissure  ;  below,  by  the  first  temporal  or  parallel 
fissure,  which  it  surrounds.  It  is  connected  posteriorly  with  the 
middle  occipital  gyrus  by  a  small  annectant  convolution.  The 
angular  evrus  of  the  left  side  is  of  considerable  clinical  and 
physiologic  interest,  because  in  man  it  is  the  center  for  the 
visual  memories  of  written  language,  and  in  the  lower  animals 
it  is  the  center  for  the  memories  of  objects  seen.  ^\\^  post- 
patnetal gyims  is  that  part  of  the  inferior  parietal  lobule  which 
surrounds  the  end  of  the  second  temporal  fissure. 


THE  OCCIPITAL  LOBE. 

The  occipital  lobe  is  pyramidal  in  shape,  forms  the  posterior 
extremity  of  the  hemisphere,  rests  upon  the  tentorium  cerebelli, 
is  situated  behind  the  parietal  lobe,  and  above  and  behind  the 
temporosphenoid.  It  is  connected  with  these  two  latter  by 
small  annectant  gyri.  It  is  separated  in  front  from  the  parietal 
lobe  by  the  external  parieto-occipital  fissure  ;   below,  it  is  con- 


FORE-BRAIN  OR  PROSENCEPHALON.  309 

nected  with  the  posterior  part  of  the  temporosphenoid  lobe. 
Its  median  surface  forms  the  posterior  margin  of  the  superior 
longitudinal  fissure,  and  it  is  separated  in  front  from  the  quad- 
rate lobe  by  the  internal  parieto-occipital  fissure,  and  behind 
from  the  temporal  lobe  by  the  calcarine  fissure.  The  occipital 
lobe  is  subdivided  into  three  smaller  convolutions  or  gyri  by 
two  constant  sulci — the  anterior  supernor  or  vertical  occipital 
sulcus,  and  the  lateral  or  inferior  occipital  sulcus.  The  former 
begins  near  the  end  of  the  lateral  sulcus,  from  which  it  is 
separated  by  the  inferior  parietal  annectant  gyrus.  It  passes 
upward  and  forward,  and  ends  just  back  of  the  external  parieto- 
occipital fissure.  Occasionally  this  fissure  is  joined  by  the  pos- 
terior limb  of  the  intraparietal  fissure.  Frequently,  it  becomes 
continuous  with  the  end  of  the  horizontal  part  of  the  intra- 
parietal fissure.  This  sulcus  separates  the  first  or  superior 
occipital  convolution  from  the  second.  The  lateral  or  inferior 
occipital  sulcus  runs  obliquely  upward  and  backward,  where  it 
branches  Y-shaped,  one  branch  passing  to  the  extreme  end  of 
the  occipital  lobe  ;  the  other  passes  downward  toward  the  cal- 
carine fissure,  where  it  ceases.  This  sulcus  separates  the  second 
from  the  third  occipital  convolution. 

The  Occipital  Convolutions. — T\\^  first  or  superior  occip- 
ital gyrus  is  superior  and  mesial  to  the  anterior  occipital 
sulcus.  Its  general  direction  is  from  below  upward.  It  brings 
the  occipital  lobe  into  relation  with  the  parietal  by  means  of 
the  first  annectant  gyrus.  The  second  or  middle  occipital  is 
beneath  the  superior  gyrus  and  between  the  anterior  and  in- 
ferior occipital  sulci.  It  is  much  broader  than  the  one  above, 
and  is  somewhat  quadrangular  in  outline.  It  is  connected  with 
the  angular  gyrus  by  the  second  annectant  convolution,  and 
with  the  middle  temporal  by  the  third  annectant  convolution. 
The  third  or  inferior  occipital  convolution  is  situated  below  and 
behind  the  middle,  from  which  it  is  separated  by  the  inferior 
occipital  sulcus.  It  forms  the  extreme  posterior  and  inferior 
portion  of  the  occipital  lobe.  It  is  connected  with  the  lower 
temporosphenoid  convolution  by  the  fourth  annectant  gyrus. 


3IO 


CENTRAL  NERVOUS  SYSTEM. 


THE    IXSUI-A,    OR    ISLAND  OF    RP:iL. 

Deep  in  the  Sylvian  fissure,  on  the  side  of  the  cerebrum  and 
near  its  base,  is  a  group  of  small  convolutions  which  were  in 
embryonic  life  a  part  of  the  cortex,  but  now  appear  subcortical, 
being  entirely  concealed  from  view  by  the  margins  of  the  Sylvian 
fissure — the  operculum.  This  small  group  of  convolutions  is 
called  the  insula,  or  island  of  Reil,  because  of  its  being  isolated 
from  the  rest  of  the  cerebral  cortex,  it  being  covered  over  by 
the  opercula  which  are  formed  by  the  following  parts — viz.,  the 
posterior  margin  of  the  third  frontal  forming  the  anterior 
operculum  ;  the  lower  margin  of  the  central  convolutions,  the 
superior  operculum  ;  and  the  apex  of  the  temporosphenoid  lobe, 
the  inferior  operculum.  In  a  general  way,  when  the  operculum 
is  referred  to,  the  superior  operculum  is  meant. 

The  gyri  which  compose  the  insula  can  only  be  seen  when 
the  margins  of  the  Sylvian  fissure  are  spread  apart  or  cut 
away.  They  originate  in  the  Sylvian  fossa,  a  little  outside  of 
the  anterior  perforated  space,  and  appear  as  a  triangular  area  of 
gray  matter,  the  base  of  which  is  upward  and  the  apex  down- 
ward and  inward.  The  apex  is  distinctly  elevated,  and  separates 
the  fossa  from  the  fissura  Sylvii.  This  area  is  separated  from  the 
opercula  by  a  fissure, — the  sulcus  limitans  insulse, — and  is  beset 
with  several  small,  shallow  sulci,  which  radiate  fan-shaped  from 
the  apex  to  the  base.  One  is  deeper  than  the  rest,  and  serves  to 
subdivide  this  region  into  two  divisions — a  precentral  and  a  post- 
central lobule.  This  is  the  central  sulcus,  or  sulcus  centralis 
insulse,  which  has  a  direction  much  like  the  overlying  fissure 
of  Rolando,  and  is  developed  at  the  same  time.  The  insula 
consists  of  a  cluster  of  from  five  to  seven  small  gyri — the  gyri 
operti  ;  their  general  direction  is  similar  to  the  direction  taken 
by  the  small  sulci — namely,  upward  and  forward.  The  more 
centrally  located  gyri  have  a  vertical  course.  Within  the  fissure 
of  Sylvius,  and  posterior  to  the  insula,  exist  two  or  three  small 
gyri  which  connect  the  superior  temporal  convolution  with  the 
inferior  parietal  lobe  ;  these  have  been  called  the  temporo- 
parietal convolutions. 


Fig.   153. -Photograph  of  the  Superior  Surface  of  the  Cerebrum. 
A  M  F.  Anterior  median  fissure  (longitudinal).     Mar.  Gyr.  Marginal  gyrus.     S.F.G.   Superior 
frontal  -yrus.     S.F.Fis.     Superior  frontal  fissure.     M.F.G.  Middle  frontal   gyrus.     Pre 
Sul.    Precentral   sulcus.     I.F.Fis.  Inferior  frontal  fissure.     Asc.F.G.    Ascending  frontal 
gyrus       Intra.  P.Fis.   Intraparietal    fissure.     Supra.  M.G.  Supramarginal    gyrus.      S.P.C 
Superior  parietal    convolution.       Ang.  G.     Angular    gyrus.       M.O.G.     Middle    occipital 
gyrus       I.O.G.   Inferior  occipital  gyrus.     S.O.G.   Superior  occipital  gyrus.     Ext.  P.U.^. 
External  parieto-occipital  fissure.      R.  Cerebellar    H.     Right  cerebellar  hemisphere.     S. 
Vermis.   Superior  vermis.     P.I.N.    Posterior  incised  cerebellar  notch.     L.    Cerebellar  M. 
Left  cerebellar  hemisphere.  I.F.G.  Inferior  frontal  gyrus. 


FORE-BRAIN  OR  PROSENCEPHALON.  313 

THE  TEMPOROSPHENOID  LOBE. 

The  temporosphenoid  lobe  is  the  portion  of  the  cerebrum 
which  is  located  in  the  middle  fossa  of  the  skull.  It  lies  at  a 
deeper  level  than  either  the  frontal  or  occipital  lobes,  and  is 
more  circumscribed.  It  is  bounded  above  and  in  front  by  the 
Sylvian  fissure,  which  completely  separates  it  from  the  frontal  lobe 
and  partially  from  the  anterior  part  of  the  parietal  lobe,  being 


Fig.    154. — Longitudinal   Section    through   Cerebral   Hemisphere   to   Show   the 

Centrum  Semiovale  of  the  Frontal,  Parietal,  Occipital,  and  Temporal  Lobes. 
C.  O.  F.   Centrum  semiovale  of  the  frontal  lobe.      C.  O.  P.    Centrum  semiovale  of  the  parietal 

lobe.       S.  L.  S.    Superior  limiting  sulcus.      C.  O.  O.  Centrum  semiovale  of  the  occipital 

lobe.     C.  O.  T.  Centrum  semiovale  of  the  temporal  lobe.      I.  C.  A.  Internal  carotid  artery. 

A.T.  L.  Anterior  extremity  of  temporal  lobe.      F.  S.   Sylvian  fissure.     A.  L.  S.   Anterior 

limiting  sulcus. 

connected  behind  and  above  with  the  latter  lobe.  It  blends 
behind  with  the  occipital  lobe,  being  partially  separated  from 
it  by  the  inferior  occipital  fissure.  The  area  in  which  both  are 
blended  is  called  the  occipitotemporal  region.  Its  external 
surface  presents  three  gyri — the  first  or  superior,  the  second 
or  middle,  and  the  third  or  inferior  temporal. 

The  first  07^  superior  convolution  is  between  the  horizontal 
limb  of  the  Sylvian  fissure  above,  forming  the  inferior  boundary 
of  the  latter  fissure,  and  the  superior  temporal  sulcus  below. 


314  CENTRAL  NERVOUS  SYSTEM. 

This  gyrus  runs  Upward  and  backward,  and  is  continuous  behind 
with  the  supramarginal  and  angular  gyri.  The  superior  temporal 
sulcus — called  also  the  parallel  fissure,  because  of  its  position  with 
respect  to  the  Sylvian  fissure — runs  from  before  backward,  then 
upward,  and  ends  in  the  angular  gyrus,  which  surrounds  it. 
This  sulcus  separates  the  first  from  the  second  temporal  convo- 
lution. 

The  second  or  iniddle  tempo7'al  gyrus  is  between  the  second 
and  superior  temporal  sulci,  passes  from  before  backward  and 
upward,  and  is  continuous  with  the  lower  part  of  the  angular 
and  the  middle  occipital  gyri.  The  second  temporal  sulcus  runs 
parallel  to  the  one  above,  but  is  not  so  long  or  deep. 

The  third  or  inferior  temporal  convolution  is  below^  the  middle 
temporal  sulcus,  and  is  separated  from  the  occipitotemporal 
g}^rus  by  the  inferior  occipital  sulcus.  It  is  connected  with  the 
occipital  lobe  by  an  annectant  gyrus.'=-  The  posterior  portion 
of  the  left  superior  and  middle  temporal  gyri  contains  the 
sensory  receptive  center  for  the  auditory  memories  of  spoken 
language. 

The  median  surface  of  the  cerebral  hemispheres  presents  six 
lobes,  separated  by  five  main  fissures.  The  lobes  are  the  mar- 
ginal, gyrus  fornicatus  or  the  convolution  of  the  corpus  callo- 
sum,  the  quadrate  or  precuneus,  the  cuneate,  lingual,  uncinate,  or 
gyrus  hippocampus.  The  fissures  are  the  callosomarginal,  the 
internal  parieto-occipital,  the  calcarine,  collateral,  dentate,  or  hip- 
pocampal  fissure.  Besides  the  convolutions  and  fissures,  the 
median  surface  also  presents  the  following  structures  :  First, 
the  divided  transverse  fibers  of  the  corpus  callosum.  The 
anterior  portion  of  this  body  is  distinctly  curved,  and  hence  is 
called  the  genu,  or  knee.  The  enlarged  posterior  part  is  called 
the  splenium,  or  pad.  Between  the  two  surfaces  exists  the 
body.  Below,  and  connected  with  the  under  surface  at  the  pos- 
terior extremity,  exists  the  fornix,  whose  anterior  part  is  sepa- 
rated from  the  corpus  callosum  by  a  thin  triangular  blade  of  white 
matter, — the  septum  lucidum, — which   blends   above  with    the 


*  A  fourth  temporal  gyrus  can  be  seen  on  the  under  surface  of  the  temporal  lobe,  separated 
from  the  gyrus  above  the  third  temporal  by  the^  third  temporal  sulcus ;  below,  this  lobule  is 
bounded  by  the  collateral  fissure. 


FORE-BRAIN  OR  PROSENCEPHALON. 


J>5 


anterior  part  of  the  corpus  callosum  and  below  with  the  fornix. 
Beneath  the  fornix  is  situated  the  outer  surface  of  one  of  the 
central  ganglia,  called  the  optic  thalamus.  In  the  center  of  the 
thalamus  is  a  bundle  of  transverse  fibers,  which  brings  the  optic 
thalami  into  relation  with  each  other.  This  transverse  bundle 
of  fibers  is  known  as  the  middle  commissure.  Ventral  to  the 
fornix  exists  the  anterior  commissure. 


CONVOLUTIONS  OF  THE  MESIAL   SURFACE. 

The  marginal  gyrus  or  convolution  is  the  median  surface 
of  the  frontal  and  central  gyri.     It  forms  a  large   part  of  the 


ParacenlTol  tobulf 


Fig.   155. — Convolutions  of  the  Mesial  Surface  of  the  Cerebrum. 

boundary  of  the  longitudinal  fissure,  and  is  the  most  extensive 
convolution  of  the  median  surface  of  the  hemisphere.  It  is  sepa- 
rated from  the  underlying  convolution — the  gyrus  fornicatus — 
by  the  callosomarginal  fissure,  which  also  separates  it  from  the 
precuneus  or  quadrate  lobe,  which  lobe  forms  really  the  poste- 
rior marginal  gyrus.  In  front  of  the  upturned  end  of  the 
callosomarginal  sulcus,  anterior  to  the  quadrate  lobe  or  pre- 
cuneus, exists  the  paracentral  lobule,  it  being  the  junction  on  the 
median  surface  of  the  hemisphere  of  the  two  central  convolutions. 
It  presents  on  its  upper  surface  a  deep  and  distinct  notch,  the 


3i6  CENTRAL  NERVOUS  SYSTEM. 

beo-innine  of  the  fissure  of  Rolando.     This  lobule  is  limited   in 

o  o 

front  by  the  paracentral  sulcus,  behind  and  below  b)-  the  calloso- 
marginal  fissure.  The  marginal  gyrus  begins  at  the  base  of  the 
brain  just  in  front  of  the  anterior  perforated  space,  takes  a 
course  upward,  forward,  and  then  bends  backward  along  the 
marofin  of  the  loneitudinal  fissure,  endinof  at  the  termination  of 
the  callosomarginal  fissure. 

The  gyrus  fornicatus,  or  convolution  of  the  corpus  callosum, 
also  called  evrus  cinouli,  is  arch-like,  and  is  situated  between 
the  marginal  gyrus  above  and  the  corpus  callosum  below.  Pos- 
teriorly, it  is  connected  with  the  precuneus  or  quadrate  lobe. 
It  is  a  very  extensive  convolution,  beginning  below  at  the  base 
of  the  brain,  in  the  anterior  perforated  space.  It  then  takes  a 
curve  upward  and  backward  around  the  genu  of  the  corpus 
callosum,  forming  a  complete  arch  around  that  body.  It  then 
passes  backward  and  curves  downward,  becoming  narrowed  at 
the  isthmus  of  the  gyrus  fornicatus,  and  taking  a  direction  for- 
ward, ends  near  the  tip  of  the  inferior  part  of  the  median  surface 
of  the  temporal  lobe. 

The  quadrate  lobe,  or  precuneus,  is  somewhat  square- 
shaped,  and  situated  along  the  margin  of  the  hemisphere, 
between  the  upturned  end  of  the  callosomarginal  fissure  in 
front  and  the  internal  parieto-occipital  fissure  behind,  which 
latter  fissure  separates  it  from  the  cuneus.  It  is  continuous 
above  with  the  superior  parietal  lobule,  being  in  reality  its 
median  surface;   below,  it  is  continuous  with  the  gyrus  fornicatus. 

The  cuneus  is  that  very  important  little  wedge-shaped  or 
triangular  lobule  whose  apex  is  downward  and  forward,  and 
whose  base  broadens  out  along  the  margin  of  the  hemisphere. 
It  is  situated  between  the  internal  parieto-occipital  fissure  in 
front  and  above  and  the  calcarine  below\  When  this  region  is 
destroyed  on  either  side,  there  occurs  a  paralysis  of  the  opposite 
halves  of  the  visual  fields  ;  hence  it  is  the  half-vision  center, 
each  cuneus  receiving  visual  impulses  from  the  corresponding 
half  of  each  retina. 

The  lingual  lobule,  also  called  the  median  occipitotemporal 
gyrus,  is  bounded  above  by  the  calcarine  fissure,  which  separates 
it  from  the  cuneus,  and   below  by  the  collateral  or  occipitotem- 


FORE-BRAIN  OR  PROSENCEPHALON.  317 

poral  fissure,  which  separates  it  from  the  fourth  temporal  gyrus. 
Anteriorly,  it  is  continuous  with  the  gyrus  hippocampus. 

The  limbic  or  falciform  lobe  is  bounded  above  by  the 
callosomarginal  fissure,  below  by  the  anterior  part  of  the  col- 
lateral fissure,  and  posteriorly  by  the  postlimbic  sulcus,  which 
is  only  a  slight  vertical  branch  of  the  callosomarginal  fissure. 
The  fissures  which  serve  to  separate  the  limbic  lobe  are  together 
called  the  limbic  fissure.  This  area  includes  the  gyrus  forni- 
catus,  the  gyrus  hippocampus,  the  dentate  lobe,  the  septum 
lucidum,  fornix,  the  anterior  commissure,  the  peduncles  of  the 
corpus  callosum,  the  nerves  of  Lancisi,  or  the  striae  longitu- 
dinales,  which  form  a  rudimentary  supracallosal   gyrus,  and  a 


Fig.  156. — Section  through  Left  Gyrus  Hippocampus.     Showing  the  formation  of  the 
hippocampus  major.      Method  of  Weigert-Pal. 


rudimentary  gyrus  beneath  the  corpus  callosum,  the  gyrus  infra- 
callosus,  or  gyrus  fornicis. 

The  slender  extension  of  the  gyrus  fornicatus  into  the  temporal 
lobe  has  received  the  name  of  gyrus  hippocampus,  or  subicu- 
lum  cornu  ammonis.  It  embraces  the  lateral  aspect  of  the  crus 
cerebri,  and  is  separated  above  from  the  optic  thalamus  by  the 
dentate  or  hippocampal  fissure,  which  fissure  extends  from  the 
splenium  of  the  corpus  callosum  downward  and  forward  to  the 
uncinate  gyrus.  It  produces  in  the  descending  horn  of  the  lateral 
ventricle  an  elevation  called  the  hippocampus  major,  or  cornu 
ammonis.  Before  reaching  the  tip  of  the  temporal  lobe  the 
hippocampal  gyrus    becomes  considerably  thickened,  and  then 


3iS  CENTRAL  NERVOUS  SYSTEM. 

forms  a  recurved  portion,  whicli  looks  backward  and  inward, 
and  is  continuous  with  the  fimbria  of  the  fornix  and  die  dentate 
gyrus.  This  recurved  portion  is  called  the  uncinate  gyrus,  or 
simply  uncus.  Posteriorly,  the  gyrus  hippocampus  is  continuous 
with  the  gyrus  fornicatus  and  the  lingual  gyrus  of  the  occipital 
lobe. 

The  dentate  gyrus,  or  fascia  dentata,  is  a  narrow  convolu- 
tion with  a  toothed  or  notched  appearance, — hence  its  name, — 
located  between  the  fimbria  and  the  gyrus  hippocampus  and 
being  overlapped  by  the  former.  It  starts  just  above  the 
splenium  of  the  corpus  callosum,  between  it  and  the  gyrus 
fornicatus,  by  a  curved  lamina, — the  fasciola  cinerea, — which  is 
continuous  with  the  lateral  and  mesial  loniritudinal  striee.  It 
then  extends  forward  and  downward,  and  is  separated  from  the 
gyrus  hippocampus  ;  it  coalesces  with  the  uncinate  gyrus.  The 
fimbria  is  a  narrow  layer  of  white  matter,  belonging  to  the 
cerebral  hemisphere,  alongside  the  dentate  gyrus.  It  is  con- 
tinuous with  the  zone  of  horizontal  fibers  beneath  the  ependyma 
of  the  cornu  ammonis,  called  the  alveus,  from  which  it  receives 
an  accession  of  fibers.  It  is  continuous  above  with  the  posterior 
pillar  of  the  fornix,  being  in  part  formed  of  its  fibers.  The 
fimbria  overlaps  the  dentate  gyrus,  and  presents  on  its  mesial 
portion  a  hooked  prolongation  continuous  with  the  choroid 
plexus.  This  gyrus  is  connected  with  the  fornix  and  the  gyrus 
fornicis,  or  gyrus  infracallosus. 

The  above-described  parts  of  the  median  surface  of  the 
cerebral  hemisphere,  which  together  constitute  the  limbic  lobe, 
are  in  man  not  well  developed,  but  in  some  of  the  lower  ani- 
mals whose  sense  of  smell  is  very  acute  (osmatics)  they  are 
greatly  developed,  and  have  been  termed,  together  with  the 
olfactory  bulb,  the  rhinencephalon. 


THE    BASE    OF  THE  CEREBRAL  HEMISPHERES. 

This  region  consists  of  the  bases  of  the  anterior,  middle,  and 
posterior  lobes.  The  anterior,  which  is  the  basal  surface  of  the 
frontal  lobe,  rests  upon  the  convexity  of  the  orbit.  It  is  sepa- 
rated from  the  middle  or  temporosphenoid  lobe  by  the  Sylvian 


FORE-BRAIN  OR   PROSENCEPHALON.  319 

fissure.  The  middle  lobe  is  the  basal  surface  of  the  temporo- 
sphenoid,  and  rests  in  the  middle  fossa  of  the  base  of  the 
skull.  The  posterior  is  the  basal  surface  of  the  occipital  lobe, 
and  rests  upon  the  tentorium  cerebelli.  The  following  ana- 
tomic points  are  to  be  observed  upon  the  base  of  the  brain, 
from  before  backward — viz.,  the  longitudinal  fissure,  the  orbital 
lobe,  the  olfactory  bulb  and  tract  of  each  side,  the  corpus  cal- 
losum  and  its  peduncles,  the  anterior  perforated  space  of  each 
side,  the  Sylvian  fissure,  the  optic  chiasm,  nerves  and  tracts  on 
each  side,  the  lamina  cinerea,  the  tuber  cinereum,  the  infundib- 
ulum,  the  pituitary  body,  the  corpora  albicantia,  the  posterior 
perforated  space,  the  third  and  fourth  pair  of  cranial  nerves, 
and  the  crura  cerebri. 

The  inferior  longitudinal  fissure  divides  the  anterior  por- 
tion of  the  frontal  lobe  and  the  entire  occipital  lobe. 

The  olfactory  bulb  is,  in  man,  a  small,  rather  club-shaped 
swelling  of  gray  matter  which,  with  the  olfactory  tract,  lies  on 
the  orbital  surface  of  the  frontal  lobe  and  is  lodg-ed  in  the  sulcus 
olfactorius.  The  bulb  presents  on  its  under  surface  several 
small,  roundish  elevations,  which  are  the  transversely  divided 
olfactory  nerves  which  have  come  from  the  rod-shaped  cells  of 
the  olfactory  mucous  membrane  of  the  upper  nasal  chamber 
after  having  passed  through  the  foramina  in  the  cribriform  plate 
of  the  ethmoid  bone.  The  olfactory  bulb  contains  many  nerve- 
cells,  about  the  dendrites  of  which  these  peripheral  olfactory 
nerve-fibers  end. 

The  olfactory  tract  passes  backward  from  the  bulb  and  pre- 
sents an  inner  or  mesial  and  an  outer  or  external  root.  The 
triangular  area  seen  between  the  diverging  roots  of  the 
olfactory  tract  is  known  as  the  trigonum  olfactorium.  The 
base  of  this  cortical  area  is  backward  toward  the  anterior  per- 
forated space,  the  apex  forward  toward  the  junction  of  the  two 
roots  of  the  olfactory  tract.  Externally,  it  is  continuous  with 
the  orbital  lobe. 

The  corpus  callosum  terminates  at  the  base  of  the  brain  as 
a  narrow  concave  portion  which  is  connected  with  the  tuber 
cinereum  by  a  thin  band  of  gray  matter — the  lamina  cinerea.  It 
gives  off  two  peduncles,  which  may  be  observed  by  raising  and 


320  CENTRAL  NERVOUS  SYSTEM. 

pushing'  the  optic  chiasm  backward.  Tliey  run  obHquely  across 
the  outer  part  of  the  anterior  perforated  space  of  each  side,  and 
probably  end  near  the  apex  of  the  temporal  lobes.  Anteriorly, 
they  pass  around  the  genu  of  the  corpus  callosum  and  are  con- 
tinuous with  the  stride  longitudinales,  or  nerves  of  Lancisi. 

The  anterior  perforated  spaces,  one  on  each  side,  are 
gray  in  color,  and  are  formed  by  the  lenticular  nuclei  of  the 
corpora  striati, — which  have  come  to  the  surface  of  the  base  at 
this  point, — are  triangular  in  shape,  and  are  perforated  by 
numerous  large  and  small  blood-vessels,  which  pass  from  the 
middle  cerebral  arteries  into  the  corpora  striati.  Each  space  is 
bounded  in  front  by  the  orbital  part  of  the  frontal  lobe  and 
olfactory  tract ;  behind,  by  the  optic  tract ;  externally,  by  the 
frontal  and  temporosphenoid  lobes  and  by  the  beginning  of 
the  fossae  Sylvii.  Internally,  it  is  continuous  with  the  lamina 
cinerea. 

The  Sylvian  Fissure. — This  begins  at  the  base  of  the  brain, 
in  the  anterior  perforated  space.  Here  it  separates  the  frontal 
from  the  temporosphenoid  lobe.  This  part  of  the  fissure  is 
called  the  fossa  or  vallecula  Sylvii.  It  lodges  the  middle  cere- 
bral or  Sylvian  artery.  On  separating  the  margins  of  the 
temporosphenoid  and  frontal  lobes  which  form  the  boundaries 
of  this  fissure,  the  prominent  cluster  of  small  gyri — the  insula, 
or  island  of  Reil — may  be  seen. 

The  Optic  Chiasm  or  Decussation. — This  is  the  junction 
of  the  two  optic  nerves.  They  form  an  incomplete  decussation. 
The  fibers  comincr  from  the  inner  or  nasal  halves  of  the  two 
retinae,  which  supply  the  outer  or  temporal  halves  of  the  field 
of  vision,  decussate,  and  pass  to  the  opposite  optic  tract.  The 
fibers  comino-  from  the  outer  or  frontal  halves  of  the  retinae  do 
not  decussate,  but  pass  directly  backward  on  the  same  side,  to 
unite  with  the  nasal  fibers  from  the  opposite  sides  of  the  retinae, 
they  having  decussated  in  the  chiasm.  The  optic  chiasm  is 
located  in  the  median'  portion  of  the  base  of  the  brain,  in  front 
of  the  tuber  cinereum  and  behind  the  lamina  cinerea,  w^hich 
latter  is  a  thin  blade  of  gray  matter  extending  from  the  termi- 
nation of  the  corpus  callosum  to  the  tuber  cinereum,  and  is  con- 
tinuous on  each  side  with  the  anterior  perforated  space.      From 


Fig.  157. — Photograph  of  the  Base  of  the  Human  Brain. 
I.  L.  F.  Inferior  longitudinal  fissure.  G.  R.  Gyrus  rectus.  O.  B.  Olfactory  bulb.  O.  T. 
Olfactory  tract.  Optic  N.  Optic  nerve,  f.  L.  Base  of  frontal  lobe.  Orbital  L.  Orbital 
lobe.  S.  F.  Sylvian  fissure.  A.  P.  S.  Anterior  perforated  space.  S.  A.  Sylvian  artery. 
Op.  T.  Optic  tract.  CM.  Corpora  mammillaria.  T.  L.  Temporal  lobe.  Crus  C.  Crus 
cerebri.  3rd  N.  Third  nerve.  4tli  N.  Fourth  nerve.  Pons.  Pons  Varolii.  6th  N.  Sixth 
nerve.  O.  L.  Occipital  lobe.  8th  N.  Eighth  nerve.  Oliv.  B.  Olivary  body.  V.  A. 
Vertebral  artery.  T.  V.  Tuber  valvulse.  S.  C.  Spinal  cord.  Tonsil.  Amygdalum  or 
tonsil.  I.  P.  L.  Inferior  posterior  lobe  of  cerebellum.  S.  L.  Slender  lobe.  D.  L.  Digas- 
tric or  cuneate  lobe.  Floe.  Flocculus.  B.  A.  Basilar  artery.  Post.  C.  A.  Posterior 
cerebral  artery.  I.  P.  S.  Interpeduncular  space.  P.  C.  A.  Posterior  communicating  artery. 
T.  C.  Tuber  cinereum.  I.  C.  A.  Internal  carotid  artery.  Tri.  S.  Triradiate  sulcus  or 
fissure.     Opt.  C.    Optic  chiasm. 


FORE-BRAIN  OR  PROSENCEPHALON.  323 

the  optic  chiasm  on  each  side  the  optic  tracts  pass  backward  and 
outward  toward  the  occipital  lobe. 

The  interpeduncular  space  is  a  lozenge-shaped  space  situ- 
ated behind  the  optic  tracts,  which  form  its  anterolateral  boun- 
dary, and  in  front  of  the  crura  cerebri, — the  diverging  peduncles 
of  the  cerebrum, — which  form  its  posterolateral  boundary.  In 
this  space  exist,  from  before  backward,  the  tuber  cinereum,  the 
infundibulum,  the  pituitary  body,  the  corpora  albicantia  or 
mammillaria,  the  posterior  perforated  space,  and  the  motor 
oculi,  or  third  pair  of  cranial  nerves. 

The  tuber  cinereum  is  an  elevation  of  gray  matter  extending 
from  the  corpora  albicantia  behind  to  the  optic  chiasm  in  front, 
to  which  it  is  attached.  It  is  continuous  with  the  lamina  cinerea, 
and  forms  part  of  the  floor  of  the  third  ventricle. 

Passing  downward  and  forward  from  its  middle  portion  is  a 
hollow,  cone-shaped  process,  the  infundibulum,  which  has 
attached  to  it  the  posterior  lobe  of  the  pituitary  body.  This 
funnel-shaped  canal  communicates  with  the  cavity  of  the  third 
ventricle,  and  is  two  or  three  lines  in  length. 

The  pituitary  body,  or  hypophysis  cerebri,  is  a  reddish, 
vascular  mass  of  an  oval  shape.  It  is  situated  in  the  sella 
turcica,  in  which  it  is  retained  by  a  process  of  dura  mater 
derived  from  the  inner  wall  of  the  cavernous  sinus.  It  consists 
of  two  divisions  or  lobes — anterior  and  posterior.  They  differ 
in  their  development,  the  anterior  lobe  being  developed  from  a 
tubular  process  of  the  ectoderm  of  the  buccal  cavity.  This 
lobe  is  of  a  yellowish-gray  color,  and  is  made  up  of  a  number 
of  slightly  convoluted  tubules  or  alveoli,  which  are  lined  by 
columnar  epithelium,  often  bearing  cilia.  The  tubules  are 
united  by  a  stroma  of  connective  tissue,  which  conveys  to  the 
gland  an  abundant  blood  and  lymphatic  supply.  It  resembles 
very  closely  in  structure  the  thyroid  gland,  and,  like  the  latter, 
often  contains  colloid  material.  It  is  surrounded  by  a  connec- 
tive-tissue capsule.  The  posterior  lobe  is  an  outgrowth  from 
the  embryonic  cavity,  which  soon  becomes  that  of  the  third 
ventricle.  This  ventricle  communicates  with  the  pituitary  body, 
during  fetal  life,  by  means  of  the  infundibulum.  In  the  adult 
the  infundibulum  is  impervious,  and  is  made  up  of  a  meshwork 


324  CENTRAL  NERVOUS  SYSTEM. 

^'  connective  tissue  containing  spindle-shaped  and  branched 
cells,  some  of  which  are  pigmented.  A  very  interesting  clinical 
fact  is  that  in  the  disease  recently  described  by  Marie,  of  Paris, 
and  named  by  him  acromegalia, — and  which  is  characterized  by 
a   oreat  increase   in    the   size  of  the  head,  the   lower  jaw,  the 

o 

hands  and  feet,  and  frequently  of  other  bones,  such  as  the 
scapula,  clavicle,  sternum,  and  ribs,  the  chest  being  often  of 
enormous  proportions  and  the  spine  being  curved. — after 
death,  in  nearly  all  instances,  an  enlargement  has  been  found 
of  the  pituitary  body  which  varies  in  size,  sometimes  being  as 
laro"e  as  a  Tangerine  orange.  The  function  of  this  body  is 
absolutely  unknown.  Although  it  is  in  man  a  ducdess  gland, 
it  must,  however,  lend  to  the  economy  an  internal  secretion 
which  is  conveyed  to  the  blood  by  means  of  its  lymph  capil- 
laries. In  some  manner,  yet  unknown,  it  probably  assists  in 
the  maintenance  of  nutrition  of  the  osseous  system. 

The  Corpora  Albicantia  or  Mammillaria. —  These  are 
two  small,  round  eminences  of  white  and  gray  matter,  about  the 
size  of  a  pea,  situated  between  the  crura  cerebri,  behind  the 
tuber  cinereum  and  in  front  of  the  posterior  perforated  space. 
The  white  matter  is  arranged  superficially  in  the  form  of  a 
mande  (stratum  zonale).  and  is  formed  chiefly  by  the  anterior 
pillars  or  crura  of  the  fornix,  which,  descending  to  the  base  of 
the  brain,  are  reflected  upon  themselves  and  form  for  each  body 
a  coverino-  of  white  matter.  The  fibers  of  these  crura  termi- 
nate  among  the  nerve-cells  within  the  albicantia.  Each  of  these 
bodies  is  brought  into  relation  with  the  optic  thalamus  by  a 
bundle  of  fibers  (bundles  of  Vicq  d'Azyr,  axones  from  the 
ventral  nucleus  of  the  thalamus),  which  pass  downward  and  end 
amonor  the  nerve-cells  of  the  albicantia.  Both  of  the  above- 
mentioned  bundles  produce  a  continuous  conducting  tract  on 
each  side  between  the  ventral  nucleus  of  the  optic  thalamus  and 
the  gyrus  hippocampus  (cornu  ammonis).  The  interiors  of  the 
corpora  albicantia  contain  two  groups  of  nerve-cells,  mesial  and 
lateral,  called  their  nuclei. 

The  posterior  perforated  space  is  a  whitish-gray  area 
located  between  the  corpora  mammillaria  in  front  and  the  pons 
Varolii  behind.     Laterally  this  space  is  continuous  on  each  side 


FORE-BRAIN  OR  PROSENCEPHALON.  325 

with  the  substantia  nigra  of  the  tegmentum  of  the  crura  cerebri. 
It  forms  the  back  part  of  the  floor  of  the  third  ventricle,  and 
is  perforated  by  numerous  small  vessels, — branches  of  the 
posterior  cerebral  and  communicating  arteries, — which  pass 
into  the  interior  to  supply  the  interior  part  of  the  optic  thalamus 
and  walls  of  the  third  ventricle.  The  third  nerves  may  be  seen 
issuing  from  the  interpeduncular  space  on  each  side,  then  pass- 
ing forward  around  the  crura  cerebri. 

The  crura  cerebri,  or  peduncles  of  the  cerebrum,  are  seen 
on  each  side  of  the  interpeduncular  space,  forming  the  outer 
boundary.  Below,  they  are  lost  among  the  fibers  of  the  pons. 
Above,  they  break  up  into  numerous  tracts,  which  radiate  toward 
the  cerebral  cortex  and  the  central  ganglia.  They  are  two  very 
thick  cylindric  masses  about  three  centimeters  in  length,  and 
composed  of  large  bundles  of  medullated  nerve-fibers.  They 
diverge  in  their  course  from  below  upward,  and  before  entering 
the  hemisphere  they  are  crossed  by  the  optic  tracts.  The  fourth 
nerves  may  be  seen  winding  around  their  outer  parts,  almost 
meeting  the  third  nerves  near  their  median  surface,  as  the  latter 
nerves  curve  around  their  inner  parts.  The  crura  cerebri  enter 
the  inner  side  of  each  hemisphere,  and  their  fibers  spread  out 
between  the  optic  thalamus  and  caudate  nucleus  on  the  inside 
and  the  lenticular  nucleus  on  the  outside,  forming  the  internal 
capsule.  Then  they  spread  out  fan-shaped,  forming  the  corona 
radiata,  and  proceed  to  all  parts  of  the  cerebral  cortex.  A 
peduncle  on  transverse  section  consists  of  two  parts  of  longi- 
tudinal fibers  separated  by  an  intermediate  stratum  of  dark 
gray  matter  in  which  is  embedded  a  large  number  of  dark  pig- 
mented nerve-cells  ;  hence  its  name — the  locus  niger,  or  sub- 
stantia nigra.  .The  superficial  or  ventral  layer  is  called  the 
crusta  ;  the  deeper  or  dorsal,  the  tegmentum,  which  is  a  continua- 
tion upward  of  the  fillet  and  the  formatio  reticularis.  These  two 
layers  of  longitudinal  fibers — superficial,  or  crustal,  and  deep,  or 
tegmental — are  made  up  of  numerous  long  tracts  of  centripetal 
and  centrifugal  fibers.  The  former  pass  into  the  subthalamic 
region,  central  ganglia,  and  cerebral  cortex  ;  the  latter,  proceed- 
ing from  the  cerebral  cortex  and  central  ganglia,  pass  downward 
to  enter  the  pons,  cerebellum,  medulla,  and  spinal  cord. 


326  CENTRAL  NERVOUS  SYSTEM. 

OLFACTORY    LOBE,   KUL!],   XI:RVKS,   AND  /FRACTS. 

The  olfactory  apparatus  includes  the  regio-olfactoria,  the 
olfactory  nerves,  the  olfactory  lobe  or  bulb,  the  trigonum  olfac- 
torium,  the  olfactory  tracts,  and  the  anterior  commissure. 

The  regio-olfactoria,  or  olfactory  region,  consists  of  the  upper 
part  of  the  nasal  septum,  the  root  of  the  nose,  and  the  upper 
and  a  part  of  the  middle  turbinated  bones. 

This  region  is  covered  by  the  olfactory  mucous  membrane, 
being-  thicker  than  is  the  Schneiderian  mucous  membrane, 
covering  the  parts  below,  which  later  is  the  true  respiratory 
region,  and  is  lined  with  stratified  epithelium  bearing  cilia.  The 
olfactory  mucous  membrane  contains  two  chief  forms  of  cells — 
columnar,  non-ciliated,  strongly  pigmented,  epithelial  cells,  the 
pigment  giving  to  the  olfactory  mucous  membrane  a  brownish- 
yellow  color ;  and  true  olfactory  nerve-cells,  spindle  or  rod-like 
in  shape,  containing  spheric  nuclei.  These  olfactory  nerve- 
cells  are  situated  between  the  columnar  cells,  and  are  bipolar  in 
form,  their  short,  thick  peripheral  processes  terminating  on  the 
surface  of  the  mucous  membrane,  where  they  spread  out  in  the 
form  of  a  network,  while  their  long,  slender  central  ones  (the  fila 
olfactoria)  pass  beneath  the  epithelial  cell-layer,  to  form  the  true 
olfactory  nerves. 

The  Olfactory  Nerves. — The  olfactory  nerves,  twenty  in 
number,  consist  of  bundles  of  fine  fibers  (the  fila  olfactoria), 
which  are  the  central  coursing  axones  of  the  rod-shaped  olfac- 
tory nerve-cells  of  the  regio-olfactoria.  They  are  non-medul- 
lated  fibers,  which  course  vertically  upward  and  enter  the  cranial 
cavity  through  the  foramina  in  the  cribriform  plate  of  the  ethmoid 
bone,  to  reach  the  inferior  surface  or  ventral  part  of  the  olfactory 
bulb,  where  they  terminate  in  arborizations  about  the  dendrites 
of  the  mitral  cells  within  the  olfactory  glomeruli.  These  bipolar 
cells  resemble  closely  the  cells  of  a  posterior  spinal  ganglion, 
possessing  a  peripheral  axone  which  terminates  free  on  the  sur- 
face of  the  olfactory  mucous  membrane,  and  a  central  axone 
which  terminates  in  the  olfactory  bulb.  These  cells,  with  their 
axones  and  terminals,  form  the  peripheral  or  olfactory  neurones 
of  the  first  order. 


FORE-BRAIN  OR  PROSENCEPHALON. 


327 


The  olfactory  lobe  is  a  hollow  protrusion  or  fold  which  extends 
forward  from  the  under  surface  of  the  wall  of  the  cavity  of  the 
cerebral  hemisphere.  It  forms  a  distinct  ridge  along  the  basal 
part  of  the  hemisphere,  from  which  it  soon  separates,  being 
converted  into  a  blind,  tubular-like  diverticulum,  which  com- 
municates posteriorly  with  the  cavity  of  the  lateral  ventricle. 
This  diverticulum  is  early  separated  by  a  groove  (the  primary 


Fig.  158. — Olfactory  Lobe  of  the  Human  Brain. — [His.) — {After  Quain.) 
Bit.  Olfactory  bulb.  T.  Tract.  Tr.o.  Trigone.  R.  Rostrum  of  corpus  callosum.  p. 
Peduncle  of  corpus  callosum,  passing  into  G.s.,  gyrus  subcallosus  (diagonal  tract,  Broca). 
Br.  Broca's  area.  F.p.  Fissura  prima.  F.s.  Fissura  serotina.  C.a.  Position  of  anterior 
commissure.  L.t.  Lamina  terminalis.  Ch.  Optic  chiasma.  T.o.  Optic  tract,  p.olf. 
Posterior  olfactory  lobule  (or  anterior  perforated  space),  m.r.  Mesial  root.  l.r.  Lateral 
root  of  tract. 


fissure  of  His)  into  an  anterior  and  a  posterior  part.  From  the 
anterior  part  is  developed  the  olfactory  tract  and  bulb,  and  the 
trigonum  olfactorium.  From  the  posterior  part  is  developed  the 
posterior  olfactory  lobe,  which  comprises  the  peduncles  of  the 
corpus  callosum,  the  inner  and  outer  olfactory  roots,  and  the 
anterior  perforated  space. 

The  olfactory  lobe,  which  in  many  animals   (osmatics)  attains 
a  very  large  size,  is  in  man  rudimentary,  the  anterior  olfactory 


j28  CENTRAL   .\ERVUUS  SYSTEM. 

lobe  being"  represented  by  the  olfactory  tract  and  bnlh  and 
trigonum  olfactorium,  while  the  posterior  lobe  comprises  th*; 
gray  matter  of  the  anterior  perforated  space. 

The  olfactory  lobe  contains,  in  most  of  the  lower  animals,  a 
narrow,  central  cavity  (the  olfactory  ventricle)  lined  with  ciliated 
epithelium,  which  rests  on  a  neuroglia  basis  and  communicates 
with  the  anterior  cornu  of  the  lateral  ventricle.  In  man  no  such 
cavity  exists,  it  having  been  obliterated  by  an  overgrowth  of 
neuroglia. 

The  olfactory  bulb,  although  a  part  of  the  cerebral  cortex, 
presents  certain  peculiarities  of  structure  which  differ  from  it. 
It  is  an  oval  or  club-shaped  mass  of  gray  matter,  which  forms  a 
sort  of  elongated  cap  for  the  ventral  portion  of  the  olfactory 
tract.  The  bulb  and  tract  are  situated  in  the  olfactory  sulcus 
on  the  orbital  surface  of  the  frontal  lobe.  The  inferior  surface 
of  the  bulb  rests  on  the  cribriform  plate  of  the  ethmoid  bone, 
through  the  foramina  of  which  it  is  connected  with  the  olfactory 
nerves. 

Olfactory  Bulb :  Its  Minute  Anatomy. — The  minute 
structure  of  the  olfactory  bulb  can  be  best  studied  by  making 
sagittal  sections  through  it,  after  being  stained  by  the  method 
of  Golgi.  It  will  be  found  to  consist  of  four  well-defined  layers  ; 
these  are  from  without  inward: 

1.  The  layer  of  olfactory  nerve-fibers. 

2.  The  layer  of  olfactory  glomeruli — stratum  glomerulorum. 

3.  The  molecular  layer,  or  stratum  gelatinosum. 

4.  The  layer  of  central  nerve-fibers. 

I.  The  outer  layer,  or  layer  of  olfactory  nerve-fibers,  consists 
of  a  thin,  superficial  layer  of  non-medullated  nerve-fibers,  which 
forms  for  the  ventral  portion  of  the  bulb  a  slight  stratum 
zonale,  each  individual  fibril  being-  the  central  axone  of  a  rod- 
shaped  nerve-cell  from  the  olfactory  mucous  membrane.  The 
fibers  of  the  olfactory  nerves  pass  into  the  underlying  glomeruli. 
Each  fibril,  just  before  entering  a  glomerulus,  separates  into  two 
or  three  divisions,  which  usually  enter  a  single  glomerulus  ;  but, 
occasionally,  they  may  pass  into  two  glomeruli.  Within  the 
glomerulus  the  terminal  divisions  of  the  olfactory  fibril  frequently 
branch,  forming-  antler-like   terminations,  which  come   into  con- 


FORE-BRAIN  OR  PROSENCEPHALON. 


329 


tact  with   an   olfactory  end  brush   of   an   apical   dendrite   of  a 
mitral  cell. 

2,  The  Layer  of  Olfactory  Glomeruli  ;  the  Stratum  Gloinerulo- 
7m7n. — This  layer  contains  many  small,  roundish  bodies,  from 
30  to  50  (ti  in  diameter,  which  are  arranged  alongside  of  one 
another,  forming  a  continuous  row  beneath  the  layer  of  olfactory 
nerve  fibers  and  above  the  molecular  layer. 


i]Mfy?iw 


Layer  of  ependymal 
cells.- 


Layer  of  central  olfac- 
torv  fibers. 


\  Layer  of  mitral  cells. 


Layer  of  olfactory 
::=^  f  fibrils  (the  fila 
'^^       I        olfactoria). 


Layer  of  olfactory 
nerve-cells  from 
the  regio  olfac- 
toria. 


Fig.  159. — A  Schematic  Representation  of  the  Principal  Elements  of  the 
Olfactory  Bulb  of  a  Mammal. — [Vatt  Gekuchten.) 

Each  glomerulus  consists  of  the  terminal  arborization  of  an 
olfactory  nerve-fiber,  together  with  olfactory  end  brushes  from 
the  apical  dendrites  of  mitral  cells.  These  two  forms  of  termi- 
nals produce  an  interlacing  network  or  tuft  of  fibrils,  which 
assume  a  spheric  form.  The  glomeruli  are  nourished  by  a 
rich  capillary  plexus  of  vessels,  which  have  descended  from  the 
overlying  pia  mater. 


330 


CENTRAl.   NKRVOUS  SYSTEM. 


3.  The  Molecular  Layer,  or  Strahwi  Gelati7iosu7)i. — In  tlie  outer 
part  of  the  molecular  layer  may  be  seen  numerous  vertically 
ascending  fibers,  a  part  of  which  are  lost  in  this  layer  ;  the 
remainder  continue  upward  and  surround  the  glomeruli  by 
passing  between  them.  This  layer  also  contains  the  apical 
dendrites  of  the  large  and  small  mitral  cells,  as  well  as  the 
terminal  branches  of  the  dendrites  of  the  deeper-lying  granular 
cells. 

The  inner  part  of  the  molecular  layer  contains  two  chief  forms 
of  cell — the  deep  and  the  superficial  layers  of  mitral  cells,  which 
correspond  to  the  large  and  small  pyramidal  cells  of  other  parts 
of  the  cerebral  cortex. 

According  to  Ramon  y  Cajal,  the  apical  dendrites  of  the  large 
mitral  cells  possess  from  eighteen  to  twenty  olfactory  end 
brushes,  which  are  distributed  to  as  many  glomeruli. 

The  large  mitral  or  pyramidal  cells  are  mostly  triangular  in 
shape,  and  from  30  to  50  a  in  diameter  ;  they  are  usually  ar- 
ranged in  a  single  row  or  layer,  although  Koelliker  states  that  it 
is  common  to  find  two  or  three  layers  of  these  cells.  They  give 
oft'  two  sets  of  dendrites,  apical  and  lateral.  The  apical  den- 
drites are,  with  rare  exceptions,  single  in  man,  and  they  do  not 
branch  until  they  reach  the  interior  of  the  olfactory  glomeruli, 
each  glomerulus  receiving  but  a  single  apical  dendrite.  Within 
each  glomerulus  the  dendrite  terminates  by  breaking  up  into  a 
globular-shaped,  interwoven  mass  of  fibers,  to  form  an  olfactory 
brush  of  fibers, — pennicilli  olfactorii,  (Koelliker), — each  olfactory 
brush  of  fibers  coming  into  contact  with  the  terminal  arboriza- 
tion  of  an  olfactory  nerve-fiber.  The  lateral  dendrites  of  the 
mitral  cells,  two  or  three  in  number,  spring  from  the  lateral 
angles  of  the  cell-body,  and  pursue  a  rather  long,  horizontal 
course  parallel  to  the  row  of  mitral  cells,  and  terminate  free. 
They  form  a  layer  of  fibers  which  separates  the  deepest  part  of 
the  molecular  from  the  fourth  or  internal  layer. 

The  axis-cylinder  or  axone  of  the  large  mitral  cells  springs 
from  the  angle  at  the  base  of  the  cell-body.  It  is  a  strong,  thick 
process  which  descends  vertically  through  the  molecular  layer, 
and  between  the  granular  cells  to  the  inner  part  of  the  fourth 
layer,  where  it  bends  at  a  right  angle  and  pursues  a  horizontal 


FORE-BRAIN  OR  PROSENCEPHALON. 


331 


course  inward  (centrally),  passing  into  the  olfactory  tract.  The 
collaterals  from  the  axones  of  the  large  mitral  cells  pursue  an 
upward  course  and  terminate  free  in  the  deep  or  superficial  part 
of  the  molecular  layer. 

The  Superficial  Layer  of  Medmm  and  Small-sized  Mitral 
Cells. — These  cells  are  spindle  or  triangular  in  shape  and 
resemble  very  closely  the  large  mitral  cells,  save  that  they  are 
smaller   in   size   and   their   apical   dendrites  are  much   shorter. 


Fig.  160. — Mitral   Cells  from  a  Mouse  Twenty-four   Days  Old. — {After  Koelliker.) 
D.    Dendrites  from  mitral  cells    forming    horizontal  fibers.      M.    Deep   layer  of  mitral  cells. 
M'^.  Superficial  layer  of  mitral  cells,      n.   Axones  of  deep  mitral  cells.     Rp.  Arborizations 
of  apical  dendrites  of  the  mitral  cells  forming  brushes  of  olfactory  fibrils. 


They  possess  both  lateral  and  apical  dendrites.  The  lateral 
dendrites  pursue  an  oblique  or  horizontal  course,  ending  free. 
Each  apical  dendrite,  like  that  of  the  large  mitral  cell,  terminates 
within  an  olfactory  glomerulus,  there  breaking  up  into  a  tuft  of 
fibers.  The  axis-cylinder  processes  of  these  cells  pursue  the 
same  course  as  do  those  from  the  large  mitral  cells,  passing 
into  the  fourth  layer,  where  they  take  a  horizontal  course.  The 
axones  of  these  cells  give  off  in  their  course  fine  collaterals, 
which  have  mostly  a  horizontal  direction. 


332  CENTRAL   NERVOUS   SYSTEM. 

The  Fourth  Layer,  or  Layer  of  Central  Nerve-fibers. — The 
outer  part  of  this  layer  is  occupied  by  a  large  number  of  very 
small  granular  cells  arranged  in  rows,  between  which  pass  the 
descending  axones  of  the  mitral  cells.  These  granular  bodies 
are  triangular,  pyramidal,  or  spindle-shaped  ;  they  possess  short, 
central  branches  or  dendrites,  and  a  single,  long,  delicate,  per- 
ipheral or  apical  dendrite,  which  latter,  tow'ard  its  termination, 
frequently  forks  and  ends  in  a  brush  of  fine  fibrils  in  the  region 
of  the  glomeruli.  Both  the  central  and  peripheral  processes 
are  studded  with  gemmules.  No  axis-cylinder  processes  have 
thus  far  been  discovered  coming  from  these  cells.  Cajal  con- 
siders them  to  be  nerve-cells  whose  axis-cylinders  probably  pass 
downward.  Van  Gehuchten  thinks  they  are  misplaced  epen- 
dymal  cells,  while  Koelliker  believes  they  are  neuroglia  cells. 

The  inner  part  of  this  layer  is  mostly  occupied  by  medullated 
nerve-fibers  and  collaterals  ;  the  former  have  both  a  centrifugal 
and  a  centripetal  course.  These  fibers  pass  both  in  a  horizontal 
and  vertical  or  radial  direction.  The  vertical  fibers  have  several 
sources  :  first,  terminal  commissural  fibers  from  the  anterior 
commissure,  which  end  about  the  olfactory  glomeruli — these  are 
the  centrifugal  fibers  ;  second,  ascending  collaterals  from  the 
large  mitral  cells ;  third,  descending  axones  from  the  large, 
medium,  and  small  mitral  cells. 

The  horizontal  fibers  are  separable  into  those  which  are  a  part 
of  the  anterior  commissure  (hence  called  commissural)  and  those 
which  form  the  olfactory  tracts.  The  commissural  bundles  of 
fibers  are  located  in  the  deepest  part  of  this  layer,  adjacent  to 
the  olfactory  ventricle.  The  fibers  which  together  form  the 
olfactory  tract  are  more  superficially  located,  consisting  of  the 
axones  of  the  mitral  cells.  The  inner  border  of  the  fourth 
layer  is  lined  with  ependymal  cells. 

The  Olfactory  Tracts. — The  nerve-fibers  of  the  olfactory 
bulbs  collect  at  their  posterior  extremities  as  two  w'ell-marked 
bundles  of  fibers — the  olfactory  tracts. 

Each  olfactory  tract  forms  for  the  bulb  a  distinct  stalk  or 
pedicle,  which  is  narrowed  at  Its  point  of  emergence  from  the 
bulb  and  grows  slightly  broader  as  it  courses  backward.  It  is 
flattened  on  Its  ventral  or  inferior  surface  and  ridtred  or  convex 


Fig.  i6i. — A  Frontal  Section   through  an   Olfactory  Bulb   of  a  Six-weeks'-old 

Cat.      Showing  layer  of  granular  cells. — {After  Koelliker.) 
Ep.   Ependyma.      Gl.   Glomerule.      Kz.   Layer  of  granular  cells.     M.   Molecular  layer.      MF. 

Layer  of  medullated  fibers.     MZ.   Layer  of  mitral  cells.     Str.gr.   Granular  zone  (stratum 

granulosum). 


FORE-BRAIN  OR  PROSENCEPHALON.  335 

along  the  middle  of  its  superior  or  dorsal  surface  ;  hence  it  is 
prismatic  or  triangular  on  transverse  section.  The  olfactory 
tract  and  bulb  is  lodged  in  the  olfactory  sulcus  of  the  orbital 
lobe,  where  some  of  its  fibers  become  continuous  along  the 
inner  side  of  the  sulcus  with  the  cortex  of  the  frontal  lobe. 
The  olfactory  tract  contains  two  systems  of  fibers — the  olfactory 
fibers  proper  (the  axones  of  the  mitral  cells)  and  the  commis- 
sural fibers  from  the  anterior  commissure.  The  former  (true 
olfactory  fibers)  form  the  ventral  part  of  the  tract,  while  the 
commissural  fibers  occupy  its  dorsal  part.  The  ventral  bundle 
(true  olfactory  tract)  separates  posteriorly  into  two  roots — an 
inner  or  mesial  and  an  outer  or  lateral  ;  these  roots  diverge 
from  each  other  and  inclose  a  triangular  space  of  gray  cortex 
— the  trigonum  olfactorium. 

The  Trigonum  Olfactorium  and  Space  of  Broca. — These 
two  areas  form  a  part  of  the  cortical  gray  matter  of  the  base  of 
the  anterior  olfactory  lobe,  which  lobe  is  bounded  internally  and 
posteriorly  by  the  primary  fissure  of  His.  This  fissure  sepa- 
rates it  from  the  anterior  part  of  the  peduncle  of  the  corpus 
callosum  on  its  inner  aspect,  and  from  the  posterior  olfactory 
lobe  (anterior  perforated  space)  behind.  This  area  has  travers- 
ing it  from  before  backward  the  diverging  roots  of  the  olfactory 
tract.  That  part  of  the  area  located  between  the  olfactory  roots 
is  known  as  the  trigonum  olfactorium  ;  it  receives  many  fibers 
from  the  dorsal  part  of  the  tract,  and  forms  the  middle  or  dorsal 
root  which  comes  from  the  anterior  commissure.  The  portion 
of  gray  matter  located  between  the  internal  root  and  the 
peduncleof  the  corpus  callosum  is  called  the  Area  of  Broca  ;  it 
receives  fibers  from  the  mesial  or  inner  root. 

The  course  of  the  root-fibers  of  the  olfactory  tract  in  man  : 
The  external,  outer,  or  lateral  root  passes  obliquely  across  the 
outer  part  of  the  anterior  perforated  space  into  the  fossa  Sylvii, 
where  its  fibers  come  into  relation  with  the  gyrus  hippocampus, 
the  uncinate  gyrus,  the  cornu  ammonis,  and  probably  the 
amygdaloid  nucleus.  The  inner  or  mesial  root  passes  back- 
ward, inward,  and  upward  around  the  area  of  Broca,  to  which  it 
lends  fibers  and  then  passes  in  to  the  anterior  extremity  of  the 
gyrus   fornicatus,    its    fibers    probably  terminating    among   the 


336  CENTRAL  NERVOUS  SYSTEM. 

I))Taniidal  cells  ot  the  cortex  ot  this  entire  lobe.  It  will  thus  be 
seen  that  the  olfactory  tract  and  bulb  have  a  connection  both 
with  the  betrinnincr  and  termination  of  the  limbic  or  falciform 
lobe.  This  connection  of  the  olfactory  bulb  and  tract  with  the 
limbic  lobe  Broca  aptly  compares  to  a  tennis-racquet,  the 
olfactory  tract  corresponding  to  the  handle  and  the  limbic  lobe 
to  the  circumference  of  the  blade.  Some  of  the  fibers  of  the 
mesial  root  pass  posteriorly  beneath  the  gyrus  fornicatus  to  the 
septum  lucidum  and  fornix,  and  thence  are  continued  into  the 
white  matter  of  the  cornu  ammonis.'=' 

The  dorsal  or  middle  root  is  composed  of  commissural  fibers 
from  the  anterior  commissure  which  have  decussated  in  the 
median  line  and  pass  into  the  olfactory  tract  through  the  trigo- 
num  olfactorium,  terminating  in  the  olfactory  bulb  about  the 
trlomeruli  and  mitral  cells.  This  centrifuofal  tract  of  fibers  forms 
an  olfactory  commissure  and  connects  the  olfactory  bulb  of  one 
side  with  the  hippocampal  and  uncinate  region  of  the  opposite 
side.  Meynert  believes  that  this  root  also  contains  fibers  joining 
the  two  olfactory  bulbs,  and  thus  forms  an  olfactory  chiasm. 


THE    ANTERIOR    COMMISSURE. 

The  anterior  commissure  belongs  to  the  cerebral  hemisphere 
and  associates  in  function  those  parts  which  are  not  united  by 
the  corpus  callosum — /.  e.,  the  temporal  lobes  in  man  and  in  os- 
matics  the  entire  rhinencephalon.  Like  the  fibers  of  the  corpus 
callosum,  the  fibers  of  which  this  commissure  is  composed  are 
probably  the  axones  of  the  pyramidal  cells  of  the  cortex  of  the 
temporal  lobe  (lobus  pyriformis  in  osmatics),  the  axones  of 
one  side  passing  across  to  arborize  about  the  pyramidal  cells  of 
the  temporal  or  pyriform  lobe  of  the  opposite  side,  and  vice 
versa. 

The  anterior  commissure  is  an  arched  bundle  of  fibers  with 
its  convexity  forward  and  its  two   extremities   spread  out  fan- 


*  According  to  some  authors,  the  dorsal,  middle,  or  commissural  root  contains  only  centripetal 
fibers  (axones  of  the  mitral  cells),  which  cross  in  the  median  line  and  terminate  in  the  hippo- 
campal and  uncinate  region  of  the  opposite  side.  These  authors  leave  unexplained  the  termi- 
nation of  the  centrifugal  fibers  of  the  olfactory  tract. 


FORE-BRAIN  OR  PROSENCEPHALON.  337 

shaped.  It  is  free  in  its  middle  part,  where  it  appears  as  a 
round  bundle  which  courses  along  the  anterior  border  of  the 
third  ventricle,  crossing-  the  space  between  the  anterior  pillars 
of  the  fornix.  At  the  level  of  the  base  of  the  septum  lucidum 
and  ventral  to  the  anterior  pillars  of  the  fornix  it  passes  on  each 
side  through  the  basal  part  of  the  head  of  the  caudate  nucleus, 
and  globus  pallidus  of  the  lenticular  nucleus,  and  divides  into 
two  bundles  which  spread  out  fan-shape  and  radiate  toward  the 
cortex  of  the  temporal  lobe. 

The  two  bundles  of  which  the  anterior  commissure  is  com- 
posed are  connected — the  anterior  with  the  opposite  olfactory 
bulb,  the  posterior  with  the  opposite  temporal  lobe  ;  hence  the 
anterior  bundle  is  called  the  pars  olfactoria  ;  the  posterior,  the 
hemispheral  bundle.  The  anterior  bundle  in  man  is  very  small, 
but  in  osmatics  it  attains  a  very  great  size,  being  about  twice 
as  large  as  the  posterior  bundle.  The  fibers  of  which  this 
bundle  is  composed  probably  take  their  origin  from  the  pyra- 
midal cells  of  the  temporal  lobe  (gyrus  hippocampus  and 
uncinate  gyrus).  From  this  extensive  origin  the  fibers  pass 
inward,  converging  in  their  course  (many  passing  through  the 
external  capsule)  through  and  beneath  the  lenticular  nucleus  and 
the  basal  part  of  the  head  of  the  caudate  nucleus  ;  the  bundle 
then  curves  downward  into  the  substance  of  the  anterior  per- 
forated space,  through  which  it  passes  into  the  peduncle  of  the 
opposite  olfactory  bulb,  terminating  about  the  olfactory  glom- 
eruli and  mitral  cells.  This  fasciculus  also  contains,  according- 
to  Meynert,  fibers  which  arise  in  the  olfactory  bulb  of  one  side 
and  pass  to  the  olfactory  bulb  of  the  opposite  side,  thus  forming  a 
true  olfactory  chiasm.  Most  of  the  fibers  (those  coming  from  the 
temporal  lobe)  after  decussating,  however,  pass  to  the  olfactory 
bulb  of  the  opposite  side,  thus  establishing  a  cross-connection 
between  the  temporal  lobe  of  one  side  and  the  olfactory  bulb  of 
the  opposite  side. 

The  posterior  or  hemispheral  bundle  takes  its  origin  from  the 
pyramidal  cells  of  the  temporal  lobe  and  amygdaloid  nucleus, 
and  after  passing  through  the  external  capsule  and  lenticular 
nucleus  joins  the  middle  part  of  the  commissure,  where  its  fibers 
decussate  and  then  radiate  to  the  opposite  temporal  lobe. 


CHAPTER    IX. 

HISTOLOGY  OF  THE  CEREBRAL  CORTEX.  TOGETHER 

WITH  THE  MINUTE  ANATOMY  OF  THE 

CENTRUM   OVALE. 

THE    HISTOLOGY  OF    THE   CEREBRAL   CORTEX. 

It  a  section  be  made  at  right  angles  to  the  surface  of  the 
cerebral  hemisphere,  it  will  be  seen  to  consist  of  an  outer  zone, 
dark-red  in  color,  and  an  inner,  homogeneous,  whitish  mass. 
The  former  is  the  cortex  cerebri ;  the  latter,  a  portion  of  the 
centrum  semiovale,  or  white  matter,  of  the  hemisphere.  The 
cortex,  or  rind,  forms  a  complete  mantle  for  each  cerebral 
hemisphere  ;  it  varies  from  2  to  4  mm.  in  thickness,  being  thinnest 
at  the  bottoms  of  the  fissures  and  sulci,  and  thickest  at  the  summit 
of  the  convolutions.  Its  thickness  also  varies  as  the  situation 
of  the  section,  being  thickest  over  the  central  gyri  and  para- 
central lobules,  where  it  measures  4  mm.,  or  about  one-sixth  of  an 
inch,  and  thinnest  over  the  occipital  lobe,  where  it  is  one-half  as 
thick.  With  the  unaided  eye  or  with  a  liand-lens  the  cere- 
bral cortex,  owing  to  differences  in  color  of  its  gray  and  white 
matter,  appears  stratified,  the  layers  being  as  follows,  from 
without  inward  :  First,  the  stratum  zonale,  or  layer  of  outer 
tangential  fibers,  consisting  of  a  narrow,  white  layer  of  mostly 
horizontal  fibers,  which  are  situated  beneath  the  pia,  and  may 
be  discovered  on  a  fresh  brain  as  a  fine,  white  line,  this  layer 
being  especially  marked  on  the  convolutions  of  the  median 
and  basal  surfaces  of  the  hemisphere,  while  not  being  very 
distinct  on  the  lateral  portions  of  the  convexity  of  the  brain. 
The  second  layer  is  located  just  beneath  the  superficial  layer, 
and  is  termed  the  superficial  gray  layer.  This  layer,  when 
observed    beneath    the    microscope,    is  seen    to    be  composed 


HISTOLOGY   OF   THE   CEREBRAL   CORTEX.  339 

mostly  of  small  pyramidal  cells,  with  their  dendrites  and  the 
dendrites  from  cells  more  deeply  situated.  The  third,  or  white 
layer  of  Vicq  d' Azyr,  or  outer  line  of  Baillarger,  is  best  marked 
in  the  gyri  bordering  the  calcarine  fissure.  The  fourth,  or 
second  layer  of  gray  matter,  consists  mostly  of  large  pyra- 
midal cells.  The  fifth  layer,  or  inner  white  line  of  Baillarger,  is 
similar  to  the  third  or  outer  white  line  of  Baillarger,  both  of 
which  are  composed  of  medullated  nerve-fibers,  which  are 
probably  the  collaterals  from  the  axones  of  the  pyramidal  cells. 
Both  of  these  lines  of  Baillaro^er  form  the  middle  tangential 
fibers.  The  sixth  layer  of  the  cortex,  or  third  layer  of  gray 
matter,  gradually  blends  with  the  underlying  central  white 
matter,  and  is  composed  of  the  polymorphous  cells  and  pro- 


FiG.  162. — Sections  of  Cerebral  Convolutions. — {After  Baillai-ger,  from  Quain.) 
I.   The  appearance  of  a  section  of  a  convolution  from  the  neighborhood  of  the  calcarine  fissure. 
2.   Shows  the  six  layers  ordinarily  seen  in  the  cerebral  cortex  when  carefully  examined 
with  naked  eye. 


cesses.  The  inner  layer  of  tangential  fibers  is  just  beneath  the 
third  layer  of  gray  matter  in  the  centrum  ovale.  This  layer 
consists  of  fine  and  coarse  fibers,  which  are  arranged  into  super- 
ficial and  deep  bundles,  which  correspond  to  the  association 
bundles.  The  superficial  fibers  form  the  short,  and  the  deep 
fibers  the  long,  bundles  of  association.  This  division  into 
layers  can  not  be  distinguished  by  the  unaided  eye  in  all  parts 
of  the  cortex,  but  in  most  fresh  brains  they  may  be  easily 
differentiated.  They  are  caused  by  large  numbers  of  fine  and 
coarse  medullated  nerve-fibers  from  the  centrum  ovale  and 
from  the  various  cortical  cells.  These  fibers,  after  pursuing 
generally  a  vertical,  but  at  times  an  oblique  or  horizontal, 
course,  end   about  the   cells  of  the   cortex,  or  pass  from  those 


The  layers  of  cortical  fibers. 


Tangential  fibers 


Fibers  of  the  sec- 
ond and  third 
layers. 


'/  Cllftz 
Fig.  163. — A  Scheme  of  the  Distribution  of  Nerve-fibers  of  the  Cerkhral  Cortex. 
According  to  the  views  of  Meynert,  Obersteiner,  Edinger,  and  Dejerine. — {After-  Dejerive.) 

The  dotted  lines  serve  to  distinguish  the  different  layers  of  cells. 
340 


1790 


18i0 


.1552 


lAcy  djmr  Daiilarapr      Kollike 
I 


H.Q^ltet 


im//,t. 


Fig.  164.— a  Scheme  Showing  the  Development  of  Our  Knowledge  of  the  Differ- 
ent Cell-layers  of  the  Human  Cerebral  Cortex  from  the  Time  of  Vicq 
d'Azyr,  in  1790,  TO  the  Time  of  Cajal,  in  1890. — {A/ier  Dejerine.) 

The  first  column  represents  the  three  layers  of  Vicq  d'Azyr  (1790),  and  the  six  layers  of  Bail- 
larger  (1840).  The  second  column  shows  the  three  layers  described  by  Koelliker  (1852). 
The  third  column  represents  the  five  layers  of  Meynert  (1867),  while  the  fourth  column 
illustrates  the  four  layers  of  Cajal  (1890). 

341 


HISTOLOGY   OF    THE   CEREBRAL   CORTEX.  343 

cells  as  their  axones  to  more  distant  parts.    In  their  course  they 
separate  the  cortical  cells  into  columnar  groups. 

Special  attention  has  been  devoted  to  the  study  of  the  cere- 
bral cortex  during  the  last  decad  by  Weigert,  Bevan  Lewis, 
Golgi,  Cajal,  Retzius,  and  Nissl,  and  most  of  our  knowledge  of 
its  minute  anatomy  is  owing  to  the  introduction  by  these 
observers  of  the  more  modern  methods  of  staining.  To  Golgi 
especially  are  we  indebted,  more  than  to  any  other  worker,  for 
a  method  of  staining  which  has  resulted  in  elucidating  many 
unsolved  problems  in  the  histology  of  the  cerebral  cortex.  The 
intricate  maze  of  cells  and  fibers  of  which  the  cortex  is  com- 
posed may  be  divided,  according  to  Ramon  y  Cajal,  into  four 
distinct  layers.  According  to  some  observers  (Meynert,  Vicq 
d' Azyr,  Baillarger),  however,  six  or  more  layers  are  distinguish- 
able ;  but  it  seems  simpler  to  describe  four  layers,  and  to  men- 
tion slight  differences  as  to  size  and  shape  of  the  cells  of  the 
deepest  layer  which  have  resulted  in  the  distinction  of  the  six  or 
more  layers.  These  layers  are  as  follows :  First,  the  super- 
ficial or  molecular  layer  ;  second,  the  layer  of  small  pyramidal 
cells  ;  third,  the  layer  of  large  pyramidal  cells ;  fourth,  the  layer 
of  polymorphous  cells. 


LAYERS  OF   CORTICAL  CELLS  AND  FIBERS. 

The  superficial,  molecular,  or  outer  cortical  layer  forms 

a  very  thin  layer  just  beneath  the  pia.  It  is  composed  of  nerve- 
fibers  and  terminals,  dendritic  processes  from  the  underlying 
pyramidal  cells,  neuroglia  cells  and  fibers,  and  a  special  variety 
of  nerve-cells,  called  Cajal  cells,  from  their  discoverer.  The 
nerve-fibers  of  this  layer  pursue  mostly  a  horizontal  course,  and 
are  best  marked  in  the  deeper  part  of  this  layer  ;  they  are  very 
long,  form  the  outer  tangential  fibers,  ancl  are  the  axones  and 
collaterals  from  the  cells  of  Cajal.  This  layer  also  contains  the 
terminations  of  many  centripetal  fibers  coming  from  the  spinal 
cord,  medulla,  and  cerebellum,  as  well  as  the  terminations  of  a 
large  number  of  commissural  fibers  and  fibers  of  association.  It 
also  contains  the  axones  from  the  cells  of  Martinotti,  as  well  as 
the  apical  dendrites  of  the  pyramidal  cells,  which  end  free  in  this 


344 


CENTRAL  NERVOUS  SYSTEM. 


layer.  I  he  neuroglia  fibers  and  cells  of  this  layer  exist  just 
beneath  the  pia  mater,  where  they  form  a  distinct  layer,  and  have 
among  them  only  a  few  nerve-cells  or  fibers.  The  neuroglia 
cells  are  chiefiy  of  the  stellate  variety  ;  their  processes  are  of 
considerable  length,  and  form  a  rather  thin  but  distinct  layer  of 
horizontal  fibers.  Of  the  Cajal  cells  there  are  three  chief  varie- 
ties— the  fusiform  or  spindle-shaped,  the  triangular,  and  the  poly- 
o-onal.  These  three  varieties  exist  in  the  human  cortex  and  in 
the  cortex  of  many  of  the  lower  animals.  They  have  been 
found  by  the  author  in  the  cortex  of  the  brain  of  the  sheep  as 
well  as  in  the  brains  of  mice  and  cats.  The  fusiform  or  spindle- 
shaped  cells  have  their  long  axes  directed  horizontally.  From 
each  pole  proceeds  a  horizontal  process  of  great  length,  per- 


FiG.  165. — A  Cajal  Cei.i.  in  Course  of    Dkvelopment   ekom   Section   of   Ascending 
Frontal  Gyrus  of  a  Human  Fetus  at  Eicht  Months. — {After  Retzius.) 


fectly  smooth,  devoid  of  granules,  and  giving  off  in  its  course 
numerous  fine  branches,  which  leave  the  parent  stem  almost  at 
right  angles,  and  proceed  vertically,  many  ending  in  small  bulbs  in 
the  most  superficial  part  of  this  layer.  Others,  after  proceeding 
upward,  divide  into  two  or  more  terminating  fibrils  having  a 
horizontal  course.  The  triangular  cell  may  possess  two,  three, 
or  more  processes.  A  common  form  is  one  with  four  processes 
— two  vertical  and  two  horizontal.  The  latter  have  a  similar 
course,  and  give  off  vertical  branches,  just  as  does  the  spindle- 
cell,  which  gives  off  collaterals,  which,  with  the  axone,  pursue  a 
horizontal  course,  forming  an  outer  tangential  fiber. 

The  polygonal  cells  give  off  numerous  dendrites  and  a  single 
neuraxone,  which  proceeds  downward,  then  becomes  horizontal. 


HISTOLOGY   OF    THE   CEREBRAL   CORTEX. 


345 


Its  collaterals  pursue  the  same  course  ;  occasionally  the  neur- 
axone  comes  off  from  one  of  the  main  dendrites. 

The  second  layer,  or  layer  of  small  pyramidal  cells.  This 
layer  consists  of  numerous  small  pyramidal  cells  arranged  in 
rows  occupying  a  considerable  vertical  extent.  These  cells  are 
located  just  beneath  the  deep  horizontal  fibers  of  the  superficial 
layer.  The  individual  cells  differ  considerably  in  size  and  shape. 
A  variety  exists  in  the  deepest  part  of  this  layer  which  seems 


Fig.  i66. — Microphotograph  of  Small  Pyramidal  Cells. 


to  be  an  intermediate  form  between  the  large  and  small  pyra- 
midal cells.  In  addition  to  the  cell-groups  of  this  layer,  there 
are  found  numerous  ascending  axones  from  underlying  cells,  as 
well  as  the  apical  processes  from  the  third  or  layer  of  large 
pyramidal  cells.  The  small  pyramidal  cells  are  triangular  in 
shape,  8  to  12  ^  in  diameter,  and  contain  oval  nuclei  and 
nucleoli.  Each  cell  possesses  a  single  apical  process,  which  is 
quite  broad  near  its  connection  with  the  cell-body  and  becomes 
attenuated   as   it   passes  vertically  upward  into   the   superficial 


346  CENTRAL  NERVOUS  SYSTEM. 

layer.  In  their  course  they  yive  oft  frequent  branches,  which 
further  subdivide,  and  pursue  a  similar  course  to  the  main  pro- 
cess, which  latter  terminates  in  the  superficial  part  of  the  molecu- 
lar layer,  where  occasionally  the  process  forks.  A  few  small 
dendrites  spring  from  the  surface  of  the  cell-body.  Two  large 
dendrites  come  oft  from  the  base  of  each  cell,  each  basal  corner 
giving  rise  to  one.  They  pursue  a  course  somewhat  obliquely 
to  the  plane  of  the  vertical  fibers  of  the  cortex. 

The  dendrites  as  well  as  the  apical  processes  are  studded 
with  minute  club-shaped  protoplasmic  processes  or  gemmules. 
These  gemmules  may  be  beautifully  seen  on  the  dendrites  of 
the  pyramidal  cells  of  the  brain  of  a  mouse  or  rat.  The  apical 
processes  present  at  irregular  intervals  tuber-like  or  varicose 
swellings.  In  opposition  to  this  statement  it  should  be  stated 
that  many  observers  believe  these  tuberosities  to  be  always  of 
pathologic  import,  but,  according  to  Lenhossek,  they  are  due 
to  local  increases  of  chromophyllic  particles.  The  axones  from 
these  cells  usually  spring  from  the  middle  of  the  base  of  the 
cells.  They  are  very  fine,  perfectly  smooth,  and  of  uniform 
thickness  throughout.  They  become  medullated,  and  enter  the 
white  matter  as  medullated  nerve-fibers.  They  give  off  at 
right  angles  collaterals  which,  according  to  Cajal,  pass  upward 
to  end  in  the  superficial  layer  of  the  cortex  (Fig.  i66). 

The  third  layer,  or  layer  of  large  pyramidal  cells,  contains, 
in  addition  to  these  cells,  a  great  number  of  vertical  fibers, 
many  of  which  are  doubtless  centripetally  coursing  axones  from 
the  central  ganglia,  medulla  oblongata,  spinal  cord,  and  cere- 
bellum. Some  of  them,  with  their  collaterals,  terminate  about 
the  dendritic  processes  of  the  cells  of  this  layer,  while  others 
continue  upward  and  terminate  in  the  superficial  layer.  This 
layer  contains,  in  addition  to  its  characteristic  pyramidal  cells, 
another  class  of  cells  whose  axones  course  upward.  These  cells 
were  first  discovered  by  Martinotti,  a  pupil  of  Golgi,  and  hence 
have  received  the  name  of  Martinotti's  cells.  A  few  small  cells 
with  numerous  dendrites,  possibly  belonging  to  Golgi's  second 
type,  are  also  found  in  this  layer. 

The  transition  from  the  cells  of  the  second  to  those  of  the 
third  layer  is  a  gradual  one,  the  cells  increa-sing  in  size  as  they 


HISTOLOGY   OF    THE   CEREBRAL   CORTEX. 


347 


become  more  deeply  situated,  small  pyramidal  cells  often  being 
observed  among  the  larger  ones,  and  an  occasional  large  pyra- 
midal cell  being  seen  in  the  second  layer.  The  cells  which  are 
characteristic  of  this  layer  are  much  larger  than  those  of  the 
layer  above,  their  average  size  being  from  1 2  to  40  ^  in  diam- 
eter. Some  of  the  laro-est,  accordlno-  to  Bevan  Lewis,  are  from 
30  to  96  1.1  in  length  and  12  to  45  ^u  in  breadth.  Their  dendrites 
are  more  numerous,  and  their  apical  processes  of  much  greater 
length  than  those  of  the  second  layer.    Each  cell  possesses  a  large, 


Fig.  167. — MiCROPHOTOGRAPH  OF  Large  Pyramidal  Cells. 


oval  nucleus,  which  contains  a  nucleolus  ;  these  cells  often  contain 
a  yellowish  pigment,  found  most  frequently  near  the  base  of  the 
chief  dendrite  or  axone.  The  cell-body  is  distinctly  triangular 
or  pyramidal,  and  gives  off  numerous  dendrites,  the  largest  of 
which  proceed  from  the  angles  at  the  base  of  the  cell.  These 
latter  dendrites  frequently  branch  and  pursue  a  diagonal  course. 
The  apical  process  or  dendrite  Is  of  great  length,  broad  near  its 
point  of  connection  with  the  cell-body,  and  gradually  narrows  as 
it  ascends,  and  presents  in  its  course  beaded  swellings  or  vari- 


348 


CENTRAL   NERVOUS  SYSTEM. 


cosities.  When  it  reaches  the  outer  cortical  layer  it  usually 
forks,  each  division  breaking-  uj)  into  a  number  of  fine  terminals, 
which  assume  a  horizontal  course  continuous  with  the  super- 
ficial fibers   of  this   layer.     Occasionally,  in  man  and  in  other 


Fig.  i68. — Cells  with  Ascendi.ng  Axonks  from  the  Cortex  of  the  Gyrus  Forni- 
CATUS  OF  A   SiX-DAYS'-OLD   MousE. — [After  Kofllikev.) 


mammalia,  the  apical  process  branches  when  it  reaches  the  level 
of  the  small  pyramidal  cells,  both  divisions  continuing  upward 
into  the  outer  cortical  layer,  where  they  fork  and  then  break  up 
into   a   brush    of   terminal    filaments.       The    dendrites    are    all 


HISTOLOGY   OF    THE   CEREBRAL   CORTEX. 


349 


Studded  with  gemmules.  The  axone  or  axis-cyhnder  process 
arises  from  the  basal  surface  of  the  cell-body,  usually  close  to  its 
middle,  and  proceeds  downward,  is  perfecdy  smooth,  very  fine, 
and  has  the  longest  course  of  any  axone  in  the  central  nervous 
system.  Proceeding  from  the  cortex  it  continues  through  the 
central  ganglia,  brain-stem,  pons,  and  medulla,  to  terminate  about 
the  motor  cells  of  the  spinal  cord.      Near  its  point  of  origin   it 


Fig.  169.— Microphotograph  of  Polygonal  Cell  of  the  Fourth  Layer  of  the 
Cerebral  Cortex  of  a  Mouse's  Brain. 


gives  off  at  right  angles  several  collaterals,  some  of  which,  ac- 
cording to  Cajal,  turn  upward  and  enter  the  superficial  cortical 
layer,  where  they  are  lost  among  the  horizontal  fibers.  Both 
axones  and  collaterals  become  medullated,  the  former  entering 
the  white  matter  of  the  centrum  semiovale  as  motor  nerve- 
fibers  (Fig.  167). 

The  cells  of  Martinotti  are  found  in  the  human  cortex,  chiefly 
among  the  large  pyramidal  cells,  although  scattered  cells  of  this 
character  may  be   found  in  the  second  layer.     They  are  some- 


J50  CENTRAL  NERVOUS  SYSTEM. 

what  triangular  or  spindle-shaped,  and  to  the  casual  observer 
appear  like  inverted  pyramidal  cells.  Their  a.xones,  which  are 
very  fine,  pass  out  of  the  apex  of  the  cell  and  course  upward, 
many  of  them  reaching  the  superficial  layer,  where  they  divide, 
each  division  further  subdividing  into  a  number  of  long,  hori- 
zontal branches,  which  terminate  in  beaded  or  varicose  extremi- 
ties. They  also  give  off  collaterals,  mostly  horizontal,  some  of 
which  probably  terminate  in  the  molecular  layer.  Usually  from 
two  to  four  rather  coarse,  branching  dendrites,  which  possess 
gemmules  and  varicosities,  pass  out  from  the  base  of  the  cell- 
body  (Fig.  1 68). 

The  fourth  layer,  or  layer  of  polymorphous  cells.  In  this 
layer  one  meets  with  a  number  of  triangular,  polygonal,  small 
pyramidal,  and  spindle  cells  ;  hence  its  name  of  layer  of  poly- 
morphous cells.  The  two  most  common  varieties  of  cells  in  this 
layer  are  the  spindle  and  polygonal  cells  ;  in  fact,  this  layer  was 
formerly  termed  the  spindle-cell  layer.  The  spindle-cells  have 
the  long  axes  of  their  bodies  placed  horizontally  or  at  right 
angles  to  the  plane  of  the  vertical  fibers  of  the  cortex.  Each 
cell  gives  off  two  large  dendrites,  one  from  each  pole,  which 
pursue  either  a  horizontal  or  a  somewhat  diagonal  course.  Their 
branches,  which  are  given  off  at  short  intervals,  are  covered  with 
gemmules.  The  axone  proceeds  from  the  cell-body,  possesses 
collaterals,  and  passes  obliquely  into  the  white  matter.  The 
polygonal  cells  possess  numerous  short  dendrites  and  long,  de- 
scending axones,  the  latter  passing  into  the  white  matter.  These 
cells  are  very  abundant  in  the  cortex  surrounding  the  calcarine 
fissure.  The  axones  from  all  these  cells  become  medullated,  and 
probably  form  association  fibers. 


THE  ANATOMY  OF  THE    CORNU   AMMONIS,  OR  HIPPO- 
CAMPUS  MAJOR,    AND   THE    GYRUS    DENTATUS. 

The  hippocampal  gyrus,  also  called  the  subiculum  cornu 
ammonis,  is  situated  along  the  inferior  portion  of  the  median 
surface  of  the  temporosphenoid  lobe,  adjacent  to  the  crus 
cerebri.  It  is  the  extension  into  that  lobe  of  the  gyrus  forni- 
catus.     Just  above  it  is  located  a  deep  cleft  or  sulcus,  the  dentate 


// 


/// 


ly 


V 


Fig.  170.— Diagram  of  the  Cells  of  the  Cerebral  Cortex.— (y^/z^r  Starr.) 
T.   Superficial  or  molecular  layer,     a.   Fusiform,      b.   Triangular,     c.  Polygonal  cells  of  Cajal. 
//.  Layer  of  small  pyramidal  cells.     </.   Smallest.     ^.  Small.    /.   Medium-sized  pyramidal  cells 

with  their  axones  descending  to  the  white  matter,  giving  off  collaterals  in  their  course. 
///.   Layer  of  large  pyramidal  cells,     g.   Largest  (giant)  pyramidal  cells,     k.    Large  pyramidal 
cell  with  very  numerous  dendrites,     m.   Martinotti  cell  with  descending  dendrites  and  as- 
cending axone.     71.   Polygonal  cells. 

IV.  Deep  layer,    p.  Fusiform  cell.     (/.  Polygonal  cell. 

V.  The  white  matter  containing  axones  from  pyramidal  cells,  d,  e,f,  g,  and  from  cell  of  the 

deep  layer,  ^.     r.   Neuroglia  fiber.  ^cj 


ANATOMY   OF   CORNU   AMMONIS   AND   GYRUS   DENTATUS. 


353 


fissure,  which  is  a  continuation  of  the  transverse  fissure,  or  fis- 
sure of  Bichat.  Inferiorly  and  dorsally,  it  is  separated  from  the 
fusiform  or  inferior  occipitotemporal  gyrus  by  the  fissure  of  the 
same  name. 

The  gyrus  hippocampus  has  the  same  histologic  construction 
as  the  rest  of  the  cerebral  cortex  until  a  point  is  reached  where 
it  becomes  involuted  or  curves  dorsomesially.  This  point  is  the 
subiculum  proper.  From  this  point  on  there  is  a  peculiar  trans- 
formation of  the  histologic  elements,  they  partaking  of  the  same 
character  as  those  of  the  cornu  ammonis,  which  this  gyrus  actu- 
ally forms. 

The  cornu   ammonis  is   the   free   ventricular   portion   of   the 


Fig.  171.— Section  through  Left  Gyrus  Hippocampus.     Showing  the  formation  of  the 
hippocampus  major.      Method  of  Weigert-Pal. 

hippocampal  gyrus,  located  in  the  descending  horn  of  the  lateral 
ventricle,'  and  is  an  involution  of  the  gyrus  hippocampus,  form- 
ing the  hippocampal  or  dentate  sulcus,  located  between  it  and 
the  dentate  gyrus,  or  fascia  dentata.  The  general  course  of  the 
gyrus  is  at  first  backward  and  slighdy  inward,  forming  the  ven- 
tral or  inferior  lamina  of  the  cornu  ammonis  ;  then  forward  and 
a  little  inward,  forming  the  superior  or  dorsal  blade  of  Am- 
mon's  horn.  It  then  curves  backward  and  terminates  in  the 
cleft  or  hilum  of  the  dentate  gyrus.  It  will  thus  be  seen  that 
it  presents  in  its  course  a  sort  of  spiral  curve.  Between  the 
laminae  of  the  cornu  ammonis  is  situated  the  dentate  gyrus,  and 
overlapping  the  dorsal  or  superior  lamina  is  the  free  extremity 


554 


CENTRAL   NERVOUS  SYSTEM. 


of  the  fimbria.     F"rom  within  outward  this  structure  presents  the 
following  layers : 

First,  the  epithelial  layer,  which  is  a  part  of  the  general  ven- 
tricular epithelium — the  ependyma.  Upon  this  layer  rests  the 
choroid  plexus. 


Fig.    172.  —  MiCROPHOTOGRAPH     OF     A      FkoMAL     SECTION     THROUGH     THE     BrAIN      OF     A 

Mouse.     Showing  the  peculiar  involution  of  the  gyrus  hippocampus  as  it  forms  the  cornu 
ammonis. 


Second,  the  inner  layer  of  horizontal  fibers  continuous  with 
those  of  the  white  matter  of  the  hemisphere,  called  the  alveus. 

Third,  the  layer  of  polymorphous  cells,  or  stratum  oriens,  which 
corresponds  to  the  fourth  cortical  layer. 


ANATOMY   OF   CORNU   AMMONIS   AND   GYRUS   DENTATUS. 


355 


Fourth,  the  layer  of  pyramidal  cells,  which  represent  the  com- 
bined second  and  third  pyramidal  cell  layers  of  the  other  parts 
of  the  cortex. 

Fifth,  the  superficial  layer,  or  substantia  reticularis  alba  ot 
Arnold.  It  corresponds  to  the  outer  or  molecular  layer  of  the 
cortex,  and  contains  cells  and  fibers  similar  to  those  of  that  layer. 


Fig.    173. — 'MiCROPHOTOGRAPH  OF  CoRNU  Ammonis  of  a  Dog's    Brain.       Showing  con- 
tour and  formation  of  cornu  ammonis. 


This  layer  is  divided  into  an  outer  and  an  inner  portion.  The 
former  is  called  the  stratum  zonale,  lamina  medullaris  circumvo- 
luta,  or  stratum  moleculare.  The  latter,  which  is  much  broader, 
consists  of  bundles  of  nerve-fibers,  and  is  called  the  stratum 
lacunosum. 

The  first  or  epithelial  layer  consists  of  ciliated  epithelial  cells 


356  CENTRAL  NERVOUS  SYSTEM. 

with  short  or  long  radiating  fibers.  This  layer  rests  iii)()n  the 
alveus  and  has  resting  upon  it  the  process  of  the  choroid  plexus 
that  descends  into  the  middle  cornu. 

The  second  layer,  or  alveus,  consists  of  fine  and  coarse  hori- 
zontal fibers,  having  among  them  a  few  scattered  polymorphous 
cells  from  the  underlying  layer — the  stratum  oriens.  The  nerve- 
fibers  of  this  layer  are  the  axones  that  issue  from  the  bases  of 
the  pyramidal  cells  of  the  fourth  layer;  these  axones  become 
curved  soon  after  leaving  the  cell-bodies,  and  assume  a  horizontal 
course.  They  give  off  collaterals,  some  of  which  pass  into  the 
next  layer  and  end  among  the  polymorphous  cells  ;  others 
course  through  the  layer  of  pyramidal  cells,  ending  just  above 
them. 

The  third  layer  is  the  layer  of  polymorphous  cells,  and  is  called 
the  stratum  oriens.  This  layer  corresponds  to  the  fourth  cortical 
layer,  and  contains  cells  of  a  like  character?  This  layer  contains, 
in  addition  to  the  basal  dendrites  of  the  pyramidal  cells,  which 
possess  ascending  axones,  cells  resembling  or  identical  with  those 
of  Martinotti.  In  the  deeper  part  of  this  layer  the  spindle  or 
triangular  cells  predominate  ;  the  long  axes  of  their  cell-bodies 
are  horizontal  ;  their  axones  either  terminate  about  the  pyramidal 
cells  or  end  in  the  superficial  layer.  According  to  Cajal,  the 
cells  with  ascending  axones  pursue  a  course  between  the  den- 
drites of  the  pyramidal  cells  and  terminate  about  the  bodies  of 
these  cells  in  a  rich  plexus  of  fibrils.  A  few  axones  condnue 
into  the  deep  part  of  the  superficial  layer,  or  stratum  lacunosum. 

Fourth,  the  pyramidal  cell  layer.     This  layer  corresponds  to 

the  second  and  third   cortical   layers  or  the  layers  of  small  and 

large  pyramidal  cells  of  the  rest  of  the  cortex.     The  small  and 

large  cells  are   intermino-led  with  one  another,  there   beino-  no 
1  •    •       • 
distmction   into  layers.      The  smaller   variety  of  cells  may  be 

considered  rather  scarce.  The  larger  cells  predominate  ;  they 
are  rather  deeply  situated,  and  resemble  very  closely  the  pyr- 
amidal cells  of  other  parts  of  the  cortex.  The  bodies  are  mosdy 
triangular  or  spindle-shaped  ;  their  apical  processes  are  very 
long,  and  branch  closer  to  the  cell-body  than  is  the  case  with 
the  other  pyramidal  cells  throughout  the  cortex.  Each  branch 
leaves  the  stem  at  rather  an  acute  angrle  ;  these  branches  further 


ANATOMY   OF    CORNU    AMMONIS    AND    GYRUS    DENTATUS. 


357 


subdivide  into  branchlets,  all  of  which  become  clustered  to- 
gether into  brushes  of  dendritic  processes,  which  course  through 
the  deep  part  of  the  superficial  layer — the  stratum  lacunosum — 
and  terminate  in  horizontal  filaments  in  the  outer  part  of  the 
superficial  layer.  The  area  just  beneath  the  stratum  lacunosum, 
which  is  occupied  by  the  unbranched  or   but  slightly  branched 


Fig.   174. — MicROFHOTOGRAPH  OF  CoRNU  Ammonis  OF  A  Rat's  Brain.     Showing  three 

large  pyramidal  cells. 


apical  processes  of  the  pyramidal  cells,  is  called  the  stratum 
radiatum.  The  basal  dendrites  of  these  cells  are  much  the  same 
as  those  of  the  pyramidal  cells  to  be  found  elsewhere  in  the 
cortex,  save  that  their  processes  are  much  shorter  and  that  they 
branch  more  frequently.  The  axones  proceed  quite  as  often 
from  a  main   basal  dendrite  as  from  the  base  of  the  cell-body ; 


358 


CENTRAL  NERVOUS  SYSTEM. 


they  pass  into  the  alveus,  where  they  form  liorizontal  fibers. 
According  to  Cajal.  the  axones,  on  entering  the  alveus,  bifurcate, 
both  divisions  becoming  horizontal  and  pursuing  a  course  oppo- 
site to  each  other.  The  collaterals  given  off  from  these  axones 
terminate  about  the  polymorphous  cells  or  among  the  dendrites 
of  the  pyramidal  cells.  In  the  dorsal  or  superior  laminae  of  the 
cornu  ammonis  of  lower  animals  pyramidal  cells  exist  which  are 


v-^'^i 


Fig.   175. — MiCROPHOTOGR.Ai'ii  through  Cornu  Ammonis.     Showing  the  deep  part  of  the 
superficial  layer,  or  stratum  lacunosuni. 


very  large  ;  hence  they  are  called  giant  pyramidal  cells.  Their 
apical  processes  are  very  short  or  wanting,  the  dendrites  frequent- 
ly springing  directly  from  the  apex  of  the  cell-body  ;  the  axones 
from  these  cells  pass  into  the  fimbria.  They  give  off  collaterals 
which  pass  into  the  stratum  lacunosum  as  medullated  nerve- 
fibers,  and  terminate  about  the  ascending  dendritic  processes  of 
the  ordinary  pyramidal  cells,  thus  associating  the  giant  pyramidal 
cells  with  the  ordinary  type  of  pyramidal  cells. 


ANATOMY   OF   CORNU   AMMONIS   AND    GYRUS   DENTATUS.  359 

Fifth,  or  outer  layer  of  the  cornu  ammonis,  may  be  subdivided 
into  a  superficial  portion,  the  stratum  moleculare  or  zonale,  and  an 
inner,  the  stratum  lacuiiosuni.  This  latter  consists  of  cells  and  a 
broad  layer  of  nerve-fibers  having  a  horizontal  course — "  tangen- 
tial fibers."  The  fibers  begin  at  the  subiculum  proper  and 
course  throughout  the  entire  extent  of  the  cornu  ammonis. 
There  are  four  chief  sources  for  the  fibers  of  this  layer — namely, 
collaterals  from  the  large  and  ordinary-sized  pyramidal  cells,  col- 
laterals from  the  fibers  of  the  alveus,  from  the  ascending  axones 
from  the  polymorphous  cells,  and  axones  from  the  stellate  and 
triangular  cells  of  this  layer.  The  cells  of  this  layer  have  both 
ascending  and  descending  dendrites ;  the  former  terminate  in 
this  layer  or  in  the  stratum  zonale,  the  latter  in  the  stratum 
oriens.  The  axones  from  these  cells  have  a  horizontal  course, 
terminating  in  this  layer  or  in  the  stratum  zonale. 

The  outermost  part  of  the  superficial  layer  of  the  stratum 
zonale,  or  lamina  medullaris  involuta,  corresponds  to  the  molec- 
ular layer  of  the  rest  of  the  cortex.  This  latter  consists  of  hori- 
zontal fibers  and  spindle-  and  stellate-shaped  cells,  the  latter 
belonging  to  Golgi's  second  type.  The  axones  of  both  varieties 
of  cells  terminate  in  this  layer.  The  nerve-fibers  of  the  layer  as 
they  approach  the  subiculum  become  continuous  with  those  of 
the  stratum  lacunosum  ;  this  layer  also  contains  the  terminations 
of  the  apical  processes  of  the  pyramidal  cells. 


GYRUS  OR  FASCIA  DENTATA. 

This  small  gyrus  consists  microscopically  of  three  distinct 
layers  :  an  outer  superficial  layer,  or  stratum  zonale  ;  a  middle  or 
layer  of  small  granular  or  pyramidal-shaped  cells,  often  called  the 
stratum  granulosum  ;  and  an  inner  layer  of  polymorphous  cells. 

The  superficial  layer,  or  stratum  zonale,  consists  of  numerous 
medullated  nerve-fibers,  which  have  a  horizontal  course — "  tan- 
gential fibers."  They  consist  of  the  ascending  axones  from  the 
cells  of  the  innermost  layer,  or  layer  of  polymorphous  cells,  and 
of  collaterals  and  terminal  fibers  from  the  alveus  of  the  cornu 
ammonis.  This  layer  also  contains  the  termination  of  the  apical 
processes  of  the  granular  or  small  pyramidal  cells. 


^6o 


CENTRAL  NERVOUS  SYSTEM. 


The  middle  or  second  layer  consists  of  small  pyramidal  or 
granular  cells  ;  hence,  often  called  the  stratum  granulosum.  The 
cells  of  this  layer  are  very  small  and  are  pyramidal  or  spheric 
in  shape.  They  possess  apical  but  no  basal  dendrites.  The 
apical  processes  or  dendrites  terminate  in  the  most  superficial 


Fig.    176-.— Microphotograph    of    Section    through    Cornu    Ammonis    and    Gyrus 
Dentatus  (Rat's  Brain).    Showing  a  group  of  small  pyramidal  cells  of  the  gyrus  dentatus. 

part  of  the  stratum  zonale.  The  axones  proceed  from  the 
base  of  the  cell-bodies,  and  passing  downward  give  off,  in  the 
layer  of  polymorphous  cells,  numbers  of  collaterals,  which  form, 
deep  beneath  the  small  pyramidal  cell  layer,  a  dense  network  of 
fibers.  The  axones  continue  downward  until  they  reach  the 
region  of  the  large  pyramidal  cells  of  the  terminal  end  of  the 
cornu  ammonis.      In  their  course  they  frequently  present  vari- 


ANATOMY    OF   CORNU    AMMONIS   AND    GYRUS    DENTATUS. 


361 


cosities,  which  give  these  fibers  the  same  appearance  as  the 
moss-like  fibers  of  the  cerebelhim,  and  hence  they  are  often 
called  the  moss-fibers  of  the  fascia  dentata.  When  they  reach 
the  region  of  the  large  pyramidal  cells  of  the  terminal  end  of 
the  cornii  ammonis  they  separate  into  two  fasciculi,  one  of  which 


Fig.   177. — MiCROPHOTOGRAPH   OF  Small  Pyramidal  Cells   of  the  Gyrus  Dentatus 
AND  Their  Axones,  Forming  the  Moss-like  Fibers. 


passes  above  the  bodies  of  the  pyramidal  cells,  to  end  about 
them  and  their  apical  dendrites  ;  the  other  fasciculus  courses 
beneath  these  same  cells,  terminating  about  their  basal  dendrites. 
These  axones  are  associative  in  function,  harmonizingf  the  action 
of  the  large  pyramidal  cells  of  the  cornu  ammonis  and  those  of 
the  fascia  dentata  (Figs.  176  .and  177). 


362  CENTRAL  NERVOUS   SYSTEM. 

The  third,  or  layer  of  polymorphous  cells,  consists  ot  three 
varieties  of  cells  :  (i)  Cells  whose  axones  proceed  upward; 
(2)  those  which  pass  downward;  and  (3)  cells  of  Golcri's  second 
type.  The  bodies  of  the  cells  whose  axones  have  an  ascending 
course  are  pyramidal  in  shape  ;  they  possess  both  ascending  and 
descending-  dendrites.  The  former  course  through  the  layer 
above,  or  stratum  granulosum,  and  terminate  in  a  brush  of 
branchlets  in  the  superficial  layer.  The  latter  descend  and 
ramify  in  the  deeper  parts  of  the  third  layer.  The  axones  from 
these  cells  course  upward  and  reach  the  superficial  layer,  when 
they  pursue  a  long,  horizontal  course.  They  give  off  numerous 
descending  collaterals,  which  ramify  between  the  small  pyramidal 
cells,  thus  forming  an  intrapyramidal  plexus.  The  cells  whose 
axones  have  a  descending  course  have  a  stellate  or  spindle  form. 
Their  axones  continue  downward  through  the  layer  of  pyramidal 
cells  of  the  cornu  ammonis,  and  terminate  as  medullated  nerve- 
fibers  in  the  alveus. 

The  cells  of  Golgi's  second  type  consist  of  many  branched 
cells  whose  processes  often  reach  the  outer  layer. 


THE    CENTRUM    OVALE. 
THE    MINUTE    ANATOMY. 

A  section  made  through  the  centrum  semiovale  conveys  to 
one's  mind  no  idea  of  the  intricate  maze  or  tangle  of  fibers  of 
w^hich  the  white  matter  is  composed.  To  the  naked  eye  it  ap- 
pears as  a  homogeneous,  white  mass,  but  if  the  brain  be  prop- 
erly hardened  by  immersion  in  alcohol  for  a  long  period,  its  con- 
stituent fibers  may  be  separated  by  teasing.  By  the  most  recent 
selective  methods  of  staining,  sections  of  this  apparently  homo- 
geneous mass  of  white  matter  may  be  seen  to  consist  micro- 
scopically of  great  numbers  of  medullated  nerve-fibers  passing 
in  a  variety  of  ways.  As  a  result  of  embryologic  and  anatomic 
studies,  and  of  investigations  of  secondary  degenerations  the 
result  of  pathologic  changes,  the  following  systems  of  fibers  have 
been  differentiated  :  First,  fibers  of  association ;  second,  the 
projection  system  of  fibers  ;  and  third,  the  commissural  fibers. 
The   association    tracts   connect    near   or   distant   parts    of   the 


THE   CENTRUM   OVALE.  363 

same  hemisphere,  thus  bringing-  the  various  regions  of  the 
hemisphere  into  intimate  association  with  one  another.  The 
projection  system  connects  definite  anatomic  areas  of  the 
cerebral  cortex  with  distant  parts  lying  below.  Thus  the  tracts 
of  which  this  system   is  composed  pass   through  the   centrum 


Fig.  178.— Horizontal  Section  of  Cerebrum  above  the  Corpus  Callosum  to  show 
THE  Centrum  Ovale. — {After  Van  Gehuchten.) 

semiovale  (centrifugal  fibers),  on  their  way  to  the  central  gan- 
glia, where  a  number  of  them  end.  The  remaining  bundles  of 
fibers  pass  by  way  of  the  crura  cerebri  to  the  pons,  cerebellum, 
medulla,  and  spinal  cord.  Other  fasciculi  belonging  to  this 
system,  and  having  a  centripetal  course,  serve  to  unite  the  spinal 
cord,   cerebellum,    pons,   and    basal    ganglia   with   the   cerebral 


364  CENTRAL  NERVOUS  SYSTEM. 

cortex.  The  commissural  fibers  pass  from  one  cerebral  hemi- 
sphere to  the  other,  thus  forming  a  bond  of  union  between 
them. 

The  association  fibers  may  be  divided  into  short  and  long- 
tracts.  The  former,  or  fibrae  arcuatae  propria;,  lie  in  and  just 
beneath  the  cortex,  and  unite  closely  adjacent  cortical  areas.  It 
is  very  probable  that  most  of  the  short  fibers  of  association  are 
the  axones  from  the  Cajal  cells  of  the  molecular  layer  of  the 
cortex.  The  long  tracts  lie  deeper  beneath  the  cortex  in  the 
centrum  semiovale,  and  unite  different  lobes  of  the  hemisphere 
as  well  as  distant  parts  of  the  same  lobe.  The  association 
fibers  represent  the  axones  or  collaterals  of  nerve-cells  which 
connect  the  cells  from  wdiich  they  spring  w^ith  other  cortical  cells 
in  the  immediate  neighborhood  (short  fibers),  or  with  cells  at  a 
greater  distance  (long  bundles  of  fibers).  These  axones  and 
collaterals  end  in  minute,  tree-like  ramifications  among  the  cells 
to  which  they  are  destined.  The  short  tracts  or  bundles  of  asso- 
ciation fibers  exist  in  large  numbers  throughout  the  hemispheres. 
They  may  be  divided  into  two  forms  :  first,  tracts  of  fibers  which 
pass  beneath  the  cortex  around  the  separate  fissures,  thus 
connecting  one  convolution  with  the  two  next  adjacent  gyri 
(fibrre  propriae)  ;  second,  bundles  of  fibers  which  unite  closely 
adjacent  parts  of  the  cortex,  thus  connecting  each  individual 
gyrus  with  the  one  next  adjacent.  These  are  the  tangential 
fibers.  By  means  of  these  association  fibers  each  convolution  is 
connected  with  every  other  convolution,  thus  bringing  them  into 
mutual  relation.  It  is  almost  positive,  according  to  Cajal,  that 
most  of  the  loner  fibers  of  association  have  their  oriorin  from  the 

o  o 

fusiform  or  polygonal  cells  of  the  fourth  layer  of  the  cortex  and 
are  their  axis-cylinder  processes.  It  is  perfectly  possible,  how- 
ever, that  some  of  the  association  fibers  may  be  the  axones  or 
collaterals  of  the  pyramidal  cells.  The  long  tracts  of  associa- 
tion which  connect  distant  parts  of  the  same  hemisphere  are 
located  rather  deep  beneath  the  cortex,  in  the  centrum  semi- 
ovale, and  are  divisible  into  the  following  important  bundles  : 

The  ciiigiUum  or  bimdle  of  the  gyrus  for)iicatiis,  also  called 
the  fasciculus  arcuatus,  extends  in  an  anteroposterior  direction 
beneath  the  median  surface  of  the  hemisphere  and  above  the 


ct.  p.p. 


Pol.  P. 


Fig.  179. — Cortex  of  Human  Brain.       Showing  the  nerve-fiber  systems  and  plexuses. 

Weigert's  and  Golgi's  method  combined. — {^Afte}-  Andriezen,  from  Starr's  ''Atlas.") 
:.z.    Clear   zone.       M.P.    Molecular    plexus    in    molecular    layer.       A.   str.    Ambiguous    cell 
stratum.     Sub/n.  P.   Submolecular  plexus.      Gt.  P.  P.    Great  pyramidal  plexus.      Pol.  P. 
Polymorphic  plexus.       IV.   White  substance. 

365 


THE    CENTRUM    OVALE. 


367 


corpus  callosum,  and  constitutes  the  greater  part  of  the  white 
matter  of  the  fornicate  and  hippocampal  gyri.  It  passes  in  a 
curved  manner,  with  its  concavity  downward  and  shghtly  forward, 
between  the  frontal  and  temporal  lobes.  The  exact  origin  and 
termination  of  its  fibers  are  unknown,  but  the  following  are  the 
most  generally  accepted  views  : 

1.  Meynert  believes  that  the  anterior  extremity  of  this  bundle 
is  in  connection  with  the  amygdaloid  nucleus. 

2.  According-  to   Broca,   the  cinorulum  connects  the  internal 


Fig.  180. — Diagram  of  the  Association-fibers  of  the  Cerebral  Hemisphere. 

— [E.  A.  S.,  after  Meynert,  from  Qiiain.) 

s.   Short  association  fibers,  connecting  adjacent  gyri.    f.Ls.   Fasciculus  longitudinalis  superior. 

c.i.  Cihgulum.     fp.  Fasciculus  perpendicularis.    f.l.i.  P'asciculus  longitudinalis  inferior. 

f.ti.  Fasciculus  uncinatus.    fo.   Fornix,    f.  Fimbria.     vuVA.   Bundle  of  Vicq  d'Azyr. 


and  external  roots  of  the  olfactory  nerves,  he  comparing  this 
system  to  the  frame  of  a  tennis-racket,  the  olfactory  roots  repre- 
senting the  handle. 

3.  According  to  Beevor,  the  cingulum  may  be  divided  into 
three  distinct  fasciculi :  an  anterior  fasciculus,  which  joins  the 
anterior  perforated  space  and  internal  olfactory  root  to  the  ante- 
rior extremity  of  the  frontal  lobe ;  a  horizontal  fasciculus,  con- 
necting the  anterior  part  of  the  gyrus  fornicatus  to  the  marginal 


368  CENTRAL  NERVOUS  SVSl  KM. 

convolution  ;  and  a  posterior  fasciculus,  connecting-  the  hippo- 
campal  convolution  to  the  lingual  and  fusiform  lobules  and  to 
the  extremity  of  the  temporal  lobe. 

4.  \'on  Monakow  states  that  the  cingulum  starts  in  the  occip- 
itotemporal region  and  terminates  in  the  frontal  lobe. 

The  fasciculus  iincinatus  of  Reil  is  the  shortest  of  the  long 
bundles  of  association.  It  is  composed  of  fibers  having  their 
origin  in  the  cells  of  the  cortex  of  the  anterior  part  of  the 
first  and  second  temporal  convolutions,  which  extend  in  a  curved 
manner  just  beneath  the  isle  of  Reil  and  close  to  the  anterior 
perforated  space,  to  the  frontal  lobe,  in  the  following  manner  : 
The  external  fibers  of  this  bundle,  owing-  to  the  proximity  of 
the  inferior  frontal  and  apex  of  the  temporal  lobes,  describe  a 
very  sharp  curve  and  pass  to  the  cortex  of  the  basal  and  convex 
surface  of  the  inferior  frontal  gyrus,  while  the  internal  fibers 
present  a  more  horizontal  course  and  radiate  to  the  orbital  part 
of  the  first  and  third  frontal  gyri. 

The  superior  longitudinal  fasciculus,  or  fasciculus  arcuaius  of 
Burdac/i,  passes  through  the  centrum  semiovale,  external  to  the 
cingulum  and  beneath  the  lower  border  of  the  frontal  and  pari- 
etal convolutions,  being  situated  above  the  level  of  the  body  of 
the  corpus  callosum.  Beneath  the  supramarginal  gyrus  this 
fasciculus  curves  downward,  backward,  and  then  forward,  its 
fibers  spreading  out  fan-shaped  and  passing  between  the  fibers 
of  the  corona  radiata  and  corpus  callosum,  to  terminate,  accord- 
ing to  Meynert.  about  the  nerve-cells  of  the  cortex  of  the  con- 
vexity of  the  occipital  and  temporal  lobes.  In  front  it  terminates 
in  the  convexity  of  the  frontal  lobe,  the  exact  location  of  its 
anterior  termination  beinof  still  unsettled. 

The  Inferior  Longitudinal  Bundle. — The  fibers  of  which  this 
tract  is  composed  come  from  all  parts  of  the  cortex  of  the  oc- 
cipital lobe.  They  are  at  first  intermingled  with  the  fibers  of 
the  corona  radiata  and  corpus  callosum,  and  pass  through  the 
white  substance  to  collect  into  a  small  round  bundle,  which 
extends  downward  and  forward  just  external  to  the  descending 
horn  of  the  lateral  ventricle,  increasing  in  size,  to  enter  the  tem- 
poral lobe.  It  receives  in  its  course  accessions  of  fibers  from 
the  cuneus,  lingual,  and  fusiform  lobules.     At  its  termination   it 


THE   CENTRUM   OVALE. 


369 


radiates  fan-shaped,  giving  off  fibers  to  the  temporal  lobe,  par- 
ticularly to  its  anterior  portion. 

Fasciculus  Occipito -frontalis  {For el  and  Onufrowicz).  —  The 
discovery  of  this  tract  resulted  from  the  study  of  a  case  of  defi- 
cient development  of  the  corpus  callosum,  in  which  case  the 
tapetum  was  found  normal,  while  the  corpus  callosum  was  absent. 
This  discovery  of  Forel  and  Onufrowicz  has  been  confirmed  by 
Muratoff,  who  found  that,  after  complete  section  of  the  corpus 


OF(Tap 


H.Cilhtr 


Fig.   181. — Semidiagrammatic   Representation  to  show  the  Fasciculus  Occipito- 

FRONTALIS,   THE   T^NIA    SeMICIRCULARIS    AND    THE    FASCICULUS     UnCINATUS. — {After 

Dejerme.') 
Cge.  External  geniculate  body.  Cgi.  Internal  geniculate  body.  Coa.  Anterior  commissure. 
Fu.  Fasciculus  uncinatus.  Gh.  Ganglion  of  the  habenula.  NA.  Amygdaloid  nucleus. 
Aa.  Anterior  nucleus  of  optic  thalamus.  NC.  Head  of  caudate  nucleus.  NC''.  Tail  of 
caudate  nucleus.  NC(T).  Body  of  caudate  nucleus.  OF.  Fasciculus  occipitofrontalis. 
OF(Tap).  Part  of  the  fasciculus  occipitofrontalis  forming  the  tapetum.  pCR.  Foot  of 
corona  radiata.  Pul.  Pulvinar.  sch.  Choroid  sulcus.  Tga.  Anterior  pillar  of  fornix. 
Th  and  Th(V3).  Optic  thalamus,  tsc(lc).  Trenia  semicircularis.  tth.  Tsenia  thalami.  H. 
Optic  tract. 

callosum  in  dogs,  the  tapetum  remained  intact,  and  Kaufman 
found  the  tapetum  intact  in  a  case  of  softening  involving  the 
corpus  callosum. 

The  fibers  of  which  this  tract  Is  composed  take  their  origin 

24 


370 


CENTRAL  NERVOUS  SYSTEM. 


from  the  cortex  of  the  external  and  basal  surface  of  the  frontal 
lobe.  They  form  a  distinct  bundle,  located  beneath  and  external 
to  the  corpus  callosum  and  between  the  cingulum  and  the  supe- 
rior longitudinal  bundle,  being  separated  from  the  latter  by  the 
foot  of  the  corona  radiata.  It  describes  a  gende  curve,  with  the 
convexity  upward,  and  courses  along  the  external  angle  of  the 
lateral  ventricle  beneath  the  ependyma,  and,  after  forming  the 
tapetum,  radiates  to  the  cortex  of  the  external  and  basal  surfaces 
of  the  occipitotemporal  lobes. 


Fig.  182. — A  Scheme  to  show  the  Origin  and  Termination  of  the  Fibers  of  the 
Corpus  Caixosum. — {After  Van  Gehitchten.) 

This  tract  joins  the  occipitotemporal  lobes  with  the  frontal 
lobe  and  the  island  of  Reil,  being  connected  to  the  latter  by 
means  of  fibers  which  pass  through  the  external  capsule. 

The  Pei'pendicidar  Fasciadus  of  Werjiicke. — This  fasciculus  is 
one  of  the  shortest  of  the  long  bundles  of  association,  and,  in  a 
general  way,  extends  from  the  superior  occipital  lobule  to  the 
inferior  occipital  gyrus  and  fusiform  lobule.  This  bundle  may 
also  connect  with  the  inferior  parietal  lobe.  It  is  a  broad  fascic- 
ulus of  vertical  fibers,  whose  width  extends  from  the  point  of 
the  occipital  to  the  dorsal  part  of  the  parietal  lobe.     Von  Mon- 


THE   CENTRUM   OVALE.  371 

akow  doubts  the  existence  in  this  region  of  any  such  bundle  of 
association. 

The  fornix,  as  it  serves  the  purpose  of  an  association  tract, 
may  be  considered  here.  It  connects,  by  means  of  its  fimbria, 
the  gyrus  hippocampus  of  each  side  with  the  corresponding 
corpus  albicans,  which  latter  body  is  connected  with  the  optic 
thalamus  both  by  means  of  a  bundle  of  white  fibers  (Vicq  d'Azyr) 
and  by  the  anterior  peduncle  of  the  fornix.  Thus  the  fornix 
serves  as  a  band  of  connection  between  the  optic  thalamus  and 
the  cornu  ammonis,  through  the  gyrus  hippocampus. 

The  commissural  fibers  which  join  the  cerebral  hemispheres 
consist,  first,  of  fibers  of  the  corpus  callosum,  and,  secondly,  of 
those  of  the  anterior  commissure.  The  corpus  callosum  is  com- 
posed of  great  bundles  of  transversely  arranged  fibers  which 
spring  from  the  pyramidal  and  polygonal  cells  of  the  cerebral 
cortex,  being  their  axis-cylinder  processes  or  collaterals  (Koel- 
liker).*  The  fibers  join,  according  to  Meynert,  identical  cortical 
areas  of  the  frontal,  occipital,  and  parietal  lobes  of  both  sides, -|- 
ending  in  arborizations  about  the  pyramidal  cells  of  the  hemi- 
sphere opposite  to  their  origin,  the  temporal  lobes  being  united 
chiefly  by  means  of  the  anterior  commissure.  According  to  Sher- 
rington, there  is  a  tendency  for  the  fibers  of  the  corpus  callosum 
to  separate,  thus  bringing  distant  as  well  as  corresponding  areas 
of  the  cortex  into  relation  with  one  another.  Hamilton  states  that 
the  corpus  callosum  consists  of  projection  fibers  which  start  from 
the  cortical  cells  of  one  side,  pass  through  the  centrum  ovale, 
decussate  and  pass  into  the  other  side,  take  a  downward  course, 
divide  into  two  bundles,  the  larger  of  which  enters  the  internal 
capsule,  losing  some  of  its  fibers  in  the  optic  thalamus,  the 
remainder  passing  downward  with  the  pyramidal  fibers  into  the 

*  According  to  Dejerine,  the  body  of  the  corpus  callosum  does  not  present  as  simple  a  structure 
as  has  been  commonly  taught.  It  is  not  formed  of  regularly  placed  bundles  of  fibers,  but  of  fibers 
which  are  more  or  less  bound  together,  and  so  arranged  that  the  superficial  fibers  of  one  side, 
after  decussating,  become  the  deep  fibers  of  the  other  side,  the  anterior  fibers  of  one  hemi- 
sphere becoming  the  posterior  fibers  of  the  other  hemisphere.  It  results  from  this  double  decus- 
sation that,  if  the  corpus  callosum  contains  commissural  fibers  which  connect  and  associate 
symmetric  and  homologous  regions  of  the  two  hemispheres,  as  Reil,  Arnold,  and  Meynert 
teach,  it  also  contains  a  great  many  fibers  of  association  which  unite  asymmetric  regions  of  the 
two  hemispheres. 

•f  The  corpus  callosum  may  also  join  the  posterior  parts  of  the  temporal  lobes. 


372 


CENTRAL  NERVOUS  SYSTEM. 


pons,  medulla,  and  possibly  the  spinal  cord.  The  fibers  of  the 
smaller  bundle  pass  into  the  external  capsule,  and  possibly  unite 
with  the  anterior  commissure.  The  researches  of  Spitzka  and 
Beevor  seem  to  disprove  Hamilton's  claim. 

The  anterior  commissure  consists  of  a  band   of  transverse 
fibers  which  connects  the  temporal  lobes.    The  fibers  of  which  the 


Fig.  1S3. — MicROPHOTOGRAPH   Showing    the    Radiation   of    the  Fibers  Co.mi'Osing 
THE  Corona  Rauiata  of  a  Rat's  Brain.     Method  of  (lolgi. 

commissure  is  composed  cross  in  the  middle  line  just  ventral  to 
the  third  ventricle  and  anterior  pillars  of  the  fornix.  They  then 
take  a  curved  direction  laterally  through  the  globus  pallidus  of 
the  lenticular  nuclei  and  beneath  the  putamen.  The  fibers  then 
spread  apart  in  a  fan-shaped  manner,  to  end  among  the  cells  of 


THE    CENTRUM   OVALE.  373 

the  cortex  of  the  temporal  lobes.  In  man  a  small  fasciculus  of 
this  commissure,  derived  from  the  olfactory  tract,  connects  w^ith 
the  opposite  hippocampal  and  uncinate  gyri. 

The  cornu  ammonis  is  connected  with  its  fellow  of  the 
opposite  side  by  a  commissural  band  of  fibers — the  psalterium. 
These  fibers,  according  to  S.  Ramon,  represent  the  fine  fibers 
of  the  alveus  (inner  layer  of  horizontal  fibers  of  the  cornu  am- 
monis), which  are  the  axones  or  collaterals  of  the  pyramidal-cell 
layer  of  Ammon's  horn. 

The  Projection  System  of  Fibers. — The  various  tracts  of 
which  this  system  is  composed  have  already  been  partly  traced 
in  describingr  the  different  anatomic  divisions  of  which  the  cere- 
brospinal  axis  is  composed.  Here  they  will  be  traced  through- 
out their  entire  course.  It  will  be  remembered  that  all  the  parts 
of  the  cerebral  cortex  are  connected  by  a  projection  system  of 
fibers  with  the  optic  thalamus.  The  following  connections  have 
been  traced  through  the  careful  observations  of  von  Monakow : 

First,  the  cortex  of  the  cornu  ammonis  is  connected  with  the 
cells  of  the  anterior  tubercle  of  the  optic  thalamus  through  the 
fasciculus  of  Vicq  d'Azyr  and  through  the  fimbria  of  the  fornix. 

Second,  the  cortex  of  the  island  of  Reil,  and  that  of  the  ad- 
jacent parts  of  the  second  and  third  frontal  convolutions,  are 
in  anatomic  relation,  through  a  fasciculus  of  fibers  which  passes 
through  the  internal  capsule,  with  the  median  nucleus  of  the 
thalamus. 

Third,  the  cortex  of  the  central  convolutions  is  in  relation,  by 
a  fasciculus  of  projection  fibers  which  course  through  the  cap- 
sule, with  the  lateral  nucleus  of  the  thalamus. 

Fourth,  the  frontal  lobe  is  connected,  by  a  bundle  of  fibers 
which  pass  through  the  anterior  limb  of  the  internal  capsule,  with 
the  anterior  division  of  the  ventral  nucleus,  the  posterior  division 
of  this  nucleus  being  connected  with  the  operculum,  the  central 
gyri,  and  the  gyrus  supramarginahs. 

Fifth,  the  posterior  nucleus  of  the  thalamus  is  in  relation 
with  the  cortex  lying  between  the   temporal  and  occipital  lobes. 

Sixth,  the  pulvinar  and  external  geniculate  body,  as  well  as 
the  anterior  corpus  quadrigeminum,  are  in  anatomic  relation 
through  the  central  optic  tract — "  optic  radiation  of  Gratiolet  " — 


374 


CENTRAL  NERVOUS  SYSTEM. 


with  the  cortex  of  the  occipital  lobe,  chieH)-  the  cuneus  and  those 
parts  of  the  cortex  bordering  on  the  calcarine  fissure  ;  this  tract 
passes  through  the  extreme  posterior  part  of  the  posterior  limb 
of  the  internal  capsule. 

Seventh,  the  corpus  geniculatum  internum  of  the  thalamus  and 
the  posterior  corpus  quadrigeminum  are  in  relation  with  the 
cortex  of  the  first  and  second  temporosphenoid  gyri  by  means 
of  the  auditory  tract. 


Fig.  184. — Di.\<;k.\.m.m.\th;  Arra.ngement  of  the  rROjECTiON  Tracts  Connecting  the 

Cerebral  Coriex  with  the  Lower  Nerve-centers. — {After  Starr.) 
A.    Frontocerebellar   tract.     B.  Motor  tract.     C.    Sensory  tract.      D.  Visual  tract  from  optic 

thalamus  (OT)  to  the  occipital  lobe.      E.    Central  auditory  tract.      F.   Superior  cerebellar 

peduncle.       G.  Middle   cerebellar   peduncle.       W.    Inferior   cerebellar   peduncle.      CN. 

Caudate    nucleus.      C.Q.   Corpora    quadrigemina.      Vt.    Fourth   ventricle.     The    numerals 

refer  to  the  cranial  nerves.      J.    Eighth  nerve  nucleus. 

The  long  tracts  of  the  projection  system  of  fibers  pass  through 
the  internal  capsule  into  the  crura  cerebri,  where  they  become 
separated  into  fasciculi,  one  body  of  these  occupying  the  ventral 
part,  or  crusta,  and  the  other  the  dorsal  part,  or  tegmentum  of 
each  peduncle.  The  former  are  the  prolongations  of  the  axis- 
cylinder  processes,  or  axones,  of  the  pyramidal  cells  of  the  cortex. 
The  following  bundles  occupy  in   the   peduncle  its  anterior  por- 


THE    CENTRUM   OVALE. 


375 


tion — foot,  orcrusta:  The  frontocerebellar  tract,  the  motor  tract, 
and  a  tract  connecting  the  occipital  and  temporal  lobes  with  both 
cerebellar  hemispheres,  but  chiefly  with  the  cerebellar  hemi- 
sphere of  the  opposite  side. 

The  frontocerebellar  tract  is  composed  of  axones  from  the 
pyramidal  cells  of  the  prefrontal  lobes  ;  from  this  wide  area  of 
origin  the  fibers  from  this  tract  converge  as  they  proceed  down- 


FiG.  185. — Diagram  TO  SHOW  the  Relative  Position  of  the  Several  Motor  Tracts 
IN  THEIR  Course  from  the  Cortex  to  the  Crus. — {After  Gowers.) 

The  section  through  the  convolutions  is  vertical ;  that  through  the  internal  capsule,  I  C,  hori- 
zontal ;  that  through  the  crus  is  again  vertical.  CN.  Caudate  nucleus.  O  TH.  Optic 
thalamus.  L2  and  L3.  The  middle  and  outer  parts  of  the  lenticular  nucleus.  /,  a,  I. 
Face,  arm,  and  leg  fibers.     The  words  in  italics  indicate  the  corresponding  cortical  centers. 


ward,  backward,  and  inward,  through  the  centrum  semiovale 
and  between  the  caudate  and  lenticular  nuclei,  occupying  the 
anterior  division  or  limb  of  the  internal  capsule  ;  thence  descend- 
ing in  the  innermost  part  of  the  crusta,  or  foot  of  the  crus 
cerebri,  to  the  ventral  part  of  the  pons  Varolii,  ending  about  the 
cells  of  the  nucleus  pontis  of  the  same  side.  The  cells  of  the 
nucleus  pontis  are  joined  by  fibers  from  both   cerebellar  hemi- 


CENTRAL  NERVOUS  SYSTEM. 

spheres  ;  chiefly,  however,  from  the  cerebellar  hemisphere  of  the 
opposite  side.  These  latter  fibers  are  theaxones  from  the  cells  of 
Purkinje  of  the  same  and  of  the  opposite  side,  the  fibers  having 
decussated  in  the  raphe.  It  will  thus  be  seen  that  the  prefrontal 
lobe  is  in  anatomic  connection  with  both  cerebellar  hemi- 
spheres, but  chiefly  with  the  cerebellar  hemisphere  of  the  oppo- 
site side. 

The  motor  tracts  consist  of  two  divisions  or  neurones — a  cen- 
tral and  a  peripheral.  The  fibers  of  which  the  central  division 
of  these  tracts  are  composed  take  their  origin  from  the  motor 
area  of  the  cerebral  cortex,  and  are  the  axis-cylinder  processes, 
or  axones,  of  the  large  pyramidal  or  motor  cells  of  the  third 
layer  of  the  cortex.  The  motor  area  of  each  hemisphere  in- 
cludes the  posterior  part  of  the  prefrontal  lobe,  the  anterior 
and  posterior  central,  or,  from  their  course,  the  ascending 
frontal  and  parietal  gyri,  with  their  union  on  the  median  surface 
of  the  hemisphere,  called  the  paracentral  lobule.  It  may  be 
stated,  in  a  general  way,  that  the  upper  third  of  the  motor  area, 
including  the  paracentral  lobule,  innervates  the  muscles  of  the 
trunk  and  lower  extremity,  the  middle  third  those  of  the  upper 
extremity,  while  the  lower  third  functionates  the  muscles  of  the 
face,  tongue,  mouth,  and  larynx — all  of  the  opposite  side.  The 
posterior  part  of  the  left  third  frontal  gyrus  contains  the  mem- 
ories necessary  to  innervate  the  motor  speech  processes.  From 
this  very  extensive  cortical  area  the  axones  of  the  motor  cells 
pass  through  the  centrum  semiovale  of  Vieussens,  converging 
as  they  proceed  until  they  reach  the  internal  capsule,  where 
they  are  collected  into  distinct  bundles  which  occupy  the  an- 
terior two-thirds  of  the  posterior  division  of  the  internal  capsule, 
the  posterior  part  of  this  division  of  the  capsule  being  occupied 
by  the  sensory,  optic,  and  auditory  tracts.  It  will  be  remem- 
bered that  the  motor  centers  for  the  muscles  of  the  face,  tongue, 
mouth,  and  larynx  occupy  the  lowest  part  of  the  motor  area ; 
hence  the  fibers  which  proceed  from  the  facial  center  have  a 
course  directly  inward,  while  those  from  the  centers  located 
above — namely,  the  arm,  leg,  and  trunk — have  a  course  down- 
ward and  inward  ;  thus  the  fibers  from  the  face  become  located 
in  the  extreme  anterior  division  of  the  posterior  limb  of  the  in- 


THE   CENTRUM   OVALE. 


377 


ternal  capsule,  while  the  fibers  fi-om  the  arm,  leg,  and  trunk 
areas  are  located  just  back  of  the  facial  fibers,  in  the  order  herein 
mentioned.  In  the  left  internal  capsule  the  fibers  that  innervate 
the  motor  speech  center  pass  a  little  anterior  to  those  of  the 


Fig.  i86. — Diagram  of  the  Course  of  the  Motor  Tract  as  shown  in  a  Diagram- 
matic Horizontal  Section  through  the  Cerebral  Hemisphere,  Pons,  and 
Medulla. — i^After  Gowers. ) 

Fr.  Frontal  lobe.  Oc.  Occipital  lobe.  A  F.  Ascending  frontal,  and  A  P,  ascending  parietal 
convolutions.  P  C  F.  Precentral  fissure  in  front  of  the  ascending  frontal  convolution. 
IFF.  Interparietal  fissure.  A  section  of  the  crura  is  lettered  on  the  left  side.  S  N. 
Substantia  nigra.  Py.  Region  occupied  by  the  pyramidal  fibers  (motor  tract),  which  on 
the  right  are  shown  as  continuous  lines,  converging  in  the  white  substance  of  the  hemi- 
sphere, to  pass  through  the  posterior  limb  of  I  C,  the  internal  capsule  (the  elbow  of  which 
is  shown  at  *) — through  the  crus  and  pons,  and  to  divide  in  the  medulla  into  the  decussat- 
ing lateral  pyramidal  tract  (Ipt)  and  the  direct  anterior  pyramidal  tract  (apt).  FC.  Fronto- 
cerebellar  tract.     Py.   Pyramidal  tract.      TOC.    Temporo-occipital  cerebellar  tract. 

face.  The  fibers  of  each  motor  tract  then  enter  the  ventral  por- 
tion or  foot  of  the  crus  cerebri,  occupying  the  middle  two-fifths 
of  its  anterior  surface  ;  the  tract  then  continuing  spineward, 
reaches  the  ventral  portion  of  the  pons  Varolii,  where  each  tract 


378  CENTRAL  NERVOUS  SYSTEM. 

separates  into  several  fasciculi,  which  lie  between  the  superficial 
and  deep  transverse  pontine  fibers.  On  emerging  from  the  in- 
ferior border  of  the  pons,  these  fasciculi  are  again  collected  into  a 
distinct  bundle,  one  for  each  side,  which  form  the  fleshy  columns 
seen  on  each  side  of  the  ventral  fissure  of  the  medulla  ob- 
longata— the  anterior  pyramids.  These  continue  to  the  inferior 
portion  of  the  medulla  ;  at  this  point — namely,  in  the  region  of 
the  first  and  second  cervical  nerves — there  occurs  an  incomplete 
decussation,  the  so-called  pyramidal  or  motor  crossway.  Here 
the  majority  of  the  fibers  decussate  and  pass  to  the  opposite 
side,  while  the  minority  do  not  cross,  but  pass  down  on  the  same 
side. 

The  crossed  fibers  descend  throughout  the  entire  length  of 
the  spinal  cord,  and  occupy  an  extensive  area  in  the  posterior 
part  of  the  lateral  column  ;  in  the  cord  this  crossed  bundle  of 
fibers  receives  the  name  of  the  crossed  motor  or  pyramidal 
tract.  This  tract  decreases  in  size  from  above  downward,  owing 
to  the  fact  that  many  of  its  axones  and  their  collaterals  are  con- 
stantly bending  forward  and  inward  to  enter  the  gray  matter  of 
the  anterior  horn  of  the  same  side,  there  terminating  in  arbori- 
zations about  the  motor  cells.  The  fibers  of  the  direct  pyr- 
amidal tract — also  called  uncrossed  motor  tract — continue  down- 
ward on  the  same  side,  occupying  a  small  area  adjacent  to  the 
anterior  median  fissure.  This  bundle  of  fibers  is  called  the 
column  of  Turck,  It  usually  ceases  at  the  level  of  the  mid-dorsal 
region,  although  in  exceptional  cases  it  passes  down  to  the  lum- 
bar region  ;  in  its  descent  its  axones  and  collaterals  pass,  by 
means  of  the  anterior  commissure,  to  the  anterior  horn  of  the 
opposite  side,  ending  at  various  levels  about  the  motor  cells 
therein  contained. 

It  will  thus  be  seen  that  the  central  division  of  the  motor  tract 
consists  of  collections  of  central  motor  neurones — the  pyramidal 
cells,  with  their  dendrites  and  axones,  the  course  of  the  latter 
continuing  without  interruption  until  they  end  by  arborizing 
about  the  motor  cells  contained  in  the  anterior  cornu  of  the  side 
opposite  to  their  origin.  The  central  division  of  the  motor 
tract  also  contains  the  central  tracts  for  the  various  motor  cranial 
nerves,  which  are  as  follows  :  The  oculoniotoj\  or  tJiird pair  ;  the 


Fig.  187. — Diagram  Indicating  the  Course  of  the  Motor  and  Sensory  Fibers 
OF  THE  Spinal  Cord  and  Medulla. 

,  a.  Motor  cells  of  the  cerebral  cortex,  b,  b.  Arborizations  of  the  fibers  of  the  sensory  tract 
in  the  cerebral  cortex,  c.  Nucleus  of  the  column  of  Burdach,  showing  terminal  arboriza- 
tions of  the  long  sensory  fibers  of  the  cord.  d.  Nucleus  of  the  column  of  Goll,  showing 
terminal  arborizations  of  the  long  sensory  fibers  of  the  cord.  e.  Section  of  the  medulla, 
showing  sensory  decussation,  f.  Section  of  medulla,  showing  motor  or  pyramidal  decus- 
sation, g,  g.  Motorial  end  plates,  h.  Section  through  the  cervical  region  of  the  cord, 
showing  termination  in  the  anterior  horn  of  the  motor  fibers  of  the  direct  pyramidal  tract 
after  they  have  crossed  in  the  anterior  commissure  ;  also  fiber  of  crossed  pyramidal  tract  end- 
ing about  anterior  horn  cell  of  same  side,  z,  i.  Posterior  spinal  ganglia,  j,  k.  Sensory  fibers 
of  short  course.  /.  Sensory  fibers  of  long  course,  terminating  in  medulla,  m,  m,  ?/i.  Sen- 
sory end  organs,      n.   Section  through  lumbar  cord. 

379 


THE   CENTRUM   OVALE. 


381 


trochlearis,  ox  fourth  ;  the  motor  division  of  the  fifth,  or  trigem- 
iitus  ;  the  abducens,  or  sixth  pair  ;  the  seventh,  ox  facial ;  the 
combined  motor  divisions  of  the  glossopharyngeal  and  pneumo- 
gastric,  or  ninth  and  te7ith  podrs  ;  the  spinal  accessory,  or  eleventh  ; 
and  the  hypoglossal,  or  twelfth  pair.  The  exact  cortical  areas 
from  which  the  various  central  cranial  nerve 
tracts  arise  is  only  positively  known  for  the 
facial,  motor  division  of  the  trigeminal,  and  the 
hypoglossal ;  these  all  take  their  origin  from  the 
cortex  of  the  lowest  third  of  the  central  convo- 
lutions. These  various  tracts  occupy  the  knee 
of  the  internal  capsule,  and  in  the  crus  cerebri 
they  are  located  on  the  inner  side  of  the  pyr- 
amidal tract ;  they  continue  downward  in  the 
crus,  pons,  and  medulla,  until  they  reach  the 
level  of  their  respective  nuclei, — whose  cells 
give  origin  to  the  peripheral  divisions  of  these 
nerves, — when  they  decussate  with  their  fellows 
and  pass  to  the  nuclei  of  the  opposite  side,  end- 
ing about  their  nerve-cells.  It  is  very  probable, 
owing  to  the  fact  that  many  of  the  motor 
cranial  nerves  innervate  bilaterally  acting  mus- 
cles, that  some  of  the  fibers  do  not  decussate, 
but  end  about  the  motor  cells  of  the  same  side. 
The  partial  course  of  the  peripheral  division  of 
the  motor  cranial  nerves  has  been  discussed  else- 
where. The  peripheral  portion  of  each  motor 
tract  consists  of  the  motor  cells  of  the  anterior 
cornu,  with  their  axis-cylinder  processes,  which 
latter  form  the  anterior  spinal  nerve-roots. 
They  terminate  in  the  motor  end  organs  of  the 
various  skeletal  muscles. 

This  combination  of  motor  nerve-cells,  with 
their  axones  and  dendrites  and  their  terminal  endings  in  the 
muscles,  form  the  peripheral  motor  neurones.  There  is  thus 
formed  by  these  two  groups  of  neurones,  central  and  peripheral, 
a  funcdonally  continuous  tract  from  the  motor  cortical  region 
of  one  cerebral  hemisphere  to  the  muscles  of  the  opposite  side 
of  the  body. 


C  O  1*.  D 

Fig.  188. — Diagram 
OF  THE  Course  of 
THE  Pyramidal 
OR  Motor  Tract 
OF  THE  Right 
Hemisphere. — 
iyAfter  Gowers.) 


382  CENIRAL  NERVOUS  SYSTEM. 

The  occipital  and  temporal  lobes  are  connected  by  a  tract  with 
the  opposite  cerebellar  hemisphere  and  slightly  with  the  cerebel- 
lar hemisphere  of  the  same  side.  The  fibers  of  this  tract  are 
the  axones  from  the  pyramidal  cells  of  the  cortex  of  the  occipital 
and  temporal  lobes.  It  was  formerly  thought  that  this  fasciculus 
of  fibers,  after  passing  through  the  centrum  semiovale,  entered 
the  extreme  posterior  part  of  the  internal  capsule,  but  Flechsig 
has  proven  that  this  is  incorrect,  and  has  shown  that  they  course 
in  part  beneath  the  lenticular  nucleus  and  in  part  between  that 
nucleus  and  the  external  geniculate  body,  whence  they  enter  the 
outer  part  of  the  foot,  or  crusta,  of  the  cerebral  peduncle  and 
continue  downward  to  the  pons  Varolii  of  the  same  side,  where 
the  individual  fibers  terminate  about  the  cells  of  the  nucleus 
pontis.  The  tract  is  further  continued  to  the  cortex  of  the 
opposite  cerebellar  hemisphere  by  means  of  the  axones  of  the 
cells  of  Purkinje,  which  also  terminate  about  the  same  cells  of 
the  nucleus  pontis  after  having  decussated  in  the  raphe.  This 
tract  also  communicates  with  the  cerebellar  hemisphere  of  the 
same  side,  owing  to  the  fact  that  a  few  axones  from  the  cells  of 
Purkinje  of  that  side  terminate  without  decussating. 

The  Sensory  Tract. — This  tract  conducts  centripetally  impres- 
sions of  touch,  pain,  temperature,  and  muscular  sense  via  the 
spinal  cord,  medulla,  pons,  brain-stem,  and  basal  ganglia  to  the 
cerebral  cortex,  where  the  impressions  are  received  as  conscious 
perceptions.  It  forms  the  chief  portion  of  the  projection  system 
of  fibers  existing  in  the  dorsal  part  or  tegmentum  of  tne  crus 
cerebri. 

The  fibers  which  compose  this  tract  have  their  origin  in  the 
cells  of  the  posterior  spinal  ganglia.  Each  ganglion  cell  gives 
off  a  single  axone,  which  soon  divides,  Y-shaped,  the  thicker 
branch  passing  out  to  form  a  peripheral  sensory  nerve  and  to 
terminate  in  a  sensory  end  organ,  and  the  finer  branch,  as  a 
posterior  nerve-root,  passing  into  the  spinal  cord  just  dorsal  to 
the  substantia  gelatinosa  Rolandi,  where  it  divides  into  an 
ascendincr  and  descending:  branch. 

The  descending  branches  of  the  posterior  nerve-roots  have 
but  a  short  longitudinal  course  in  the  posterior  columns,  when 
they  curve  inward  and  terminate  in  arborizations  about  the  cells 


Fig.  iSg.—  {A/i^gr  Sac%s.) 

Fig.  I.  Sensory  tract,  a,  b.  Cells  of  spinal  ganglia,  one  fiber,/,  forming  part  of  sensory  nerve 
the  other  fiber,  c,  entering  a  posterior  root,  fibers  of  the  latter  dividing  into  ascending  and 
descending  (i,  2,  3,  4)  branches.  Of  the  ascending  branches,  some  (4)  terminate  with 
"  end-brushes  "  in  the  nucleus  cuneatus,  and  nucleus  gracilis,  col.  Collateral  fibers  enter- 
ing gray  matter.  8.  Fibers  forming  anterior  ground  bundle.  5,6.  Fibers  forming  lateral 
ground  bundle.  10.  Fib-.rs  forming  Cowers'  tract.  7.  Fibers  forming  direct  cerebellar 
tract. 

Fig.  II.  r.a.  Anterior  root.  r.p.  Posterior  root.  LR.  Lissauer's  marginal  zone.  I.  Direct 
pyramidal  tract.  2.  Anterior  ground  bundle.  3.  Lateral  ground  bundle.  4.  Cowers' 
anterolateral  tract.  5.  Crossed  pyramidal  tract.  6.  Direct  cerebellar  tract.  7.  Column 
of  Burdach.  8.  Column  of  Coll.  9.  Posterior  longitudinal  septum.  lO.  Anterior  longi- 
tudinal fissure.  II.  Anterior  median  group  of  cells.  12.  Posterolateral  group.  13. 
Column  of  Clarke. 

Fie    III.   Relation  of  motor  tract  to  nuclei  of  cranial  nerves. — {After  Flatau.) 

383 


THE   CENTRUM    OVALE.  385 

of  the  gray  matter  of  the  cord.  The  ascending  branches  con- 
sist of  two  divisions — those  which  pursue  a  rather  short  longi- 
tudinal course  and  those  which  pursue  a  long  course.  The 
former  enter  the  gray  matter  in  curves,  and  terminate  as  do  the 
descendinof  branches.  Some  of  the  branches  of  lono-  course 
pass  upward  into  the  postero-external  column,  or  column  of 
Burdach  ;  while  the  greater  number  pursue  a  similar  course  in 
the  postero-internal  column,  or  column  of  Goll.  All  these  fibers 
of  long  course  continue  upward  until  they  reach  the  lower  dor- 
sal region  of  the  medulla,  where  they  bend  nearly  at  right 
angles  and  terminate  in  brushes  of  fibrils  about  the  nerve-cells 
of  the  nucleus  cuneatus  and  nucleus  orracilis.  Both  ascending- 
and  descending  branches  are  constantly  giving  off  in  their  course 
collaterals,  which  enter  the  gray  matter  and  terminate  about  the 
intrinsic  cells  of  the  posterior  horns  and  intermediate  gray 
matter  about  the  motor  cells  of  the  anterior  horns  (reflex  col- 
laterals) and  about  the  cells  of  Clarke's  column. 

Gowers  tract,  which  is  supposed  to  conduct  sensations  of 
temperature  and  pain,  consists  of  axones  which  arise  from  the 
intrinsic  cells  located  in  the  intermediate  gray  matter  near  the 
base  of  the  anterior  horn,  around  which  cells  collaterals  from 
the  posterior  nerve-roots  terminate.  The  axones  from  this 
group  of  intrinsic  cells  pass  across  the  gray  matter,  probably  in 
the  anterior  commissure,  to  the  opposite  side  of  the  cord,  where 
they  turn  upward  and  become  located  in  the  anterolateral  per- 
iphery of  the  cord,  ventral  to  the  direct  cerebellar  and  crossed 
pyramidal  tracts.  These  fibers  course  upward  until  they  reach 
the  medulla  oblongata,  where  some  may  be  intercepted  by  the 
cells  of  the  lateral  nucleus.  The  tract  then  continues  upward  in 
the  formatio  reticularis,  where  it  occupies  a  position  dorso- 
lateral to,  the  olivary  body.  At  about  the  middle  of  the  pons 
Varolii,  according  to  Hoche,  this  bundle  makes  a  distinct  curve 
over  the  fifth  nerve  and  enters  the  cerebellum  by  means  of  the 
superior  cerebellar  peduncle  and  velum  medullare  anticum.  It 
is  extremely  probable  that  a  part  of  the  fibers  of  this  tract  con- 
tinue br^inward  in  the  formatio  reticularis,  and  terminate  in 
part  in  the  corpus  quadrigeminum,  and  in  part  in  the  optic  thal- 
amus. The  cortical  termination  of  this  part  of  the  tract  is  prob- 
25 


386  CENTRAL  NERVOUS  SYSTEM. 

ably  in  the  parietal  lobe,  the  fibers   passing  with  those   of  the 
mesial  fillet. 

The  largest  portion  of  the  sensor)-  tract,  whose  axones  have 
terminated  about  the  cells  of  the  nuclei  cuneati  and  gracili,  is 
farther  continued  by  the  axones  from  the  cells  of  these  nuclei, 
which  axones  pass  ventromesially  (internal  arcuate  fibers)  to 
the  region  between  the  olivary  bodies,  where  they  decussate, 
forming  the  interolivary  or  superior  sensory  decussation.  Each 
tract  then  turns  upward  just  dorsal  to  the  anterior  pyramids,  and 
is  now  termed  the  mesial  fillet,  lemniscus,  or  interolivary  tract. 
In  the  pons  it  occupies  the  ventral  portion  of  the  formatio  retic- 
ularis, and  continues  brainward  through  the  ventral  part  of  the 
tegmentum  of  the  crus  cerebri  to  the  subthalamic  reo-ion,  where 
a  small  part  of  the  fibers  from  the  cells  of  the  nucleus  cuneatus 
terminate  in  the  anterior  corpus  quadrigeminum.  The  main 
bundle  of  fibers  from  this  nucleus  passes  to  the  outer  side  of 
Luys'  body,  and  joins  both  the  lenticular  loop  and  Meynert's 
commissure.  The  first  part  of  the  bundle  passes  by  way  of  the 
lenticular  loop  to  the  globus  pallidus  of  the  lenticular  nucleus  of 
the  same  side,  while  the  remaining  fasciculus  passes  to  the  len- 
ticular nucleus  of  the  opposite  side  by  way  of  Meynert's  com- 
missure. The  fasciculus  of  fibers  of  the  fillet  or  lemniscus,  which 
are  the  axones  from  the  nucleus  oracilis,  g-ive  off  collaterals  which 
join  the  anterior  corpus  quadrigeminum,  ending  about  die  cells  of 
the  fifth  layer.  The  main  bundle  of  fibers  of  this  fascicuV^,  how- 
ever, continues  ventrad,  and  terminates  in  arborizations  Tibout 
the  cells  of  the  ventral  nucleus  of  the  optic  thalamus  of  the  same 
side  (von  Monakow),  the  axones  of  which  cells  continue  this  tract 
through  the  posterior  third  of  the  posterior  division  of  the  in- 
ternal capsule,  whence  they  radiate  through  the  centrum  semi- 
ov'ale  to  the  cortex  of  the  postcentral  and  parietal  lobes.  The 
sensory  tract  receives  in  its  course  axones  and  collaterals  from 
the  various  sensory  end  nuclei  of  the  cranial  nerves  of  the 
opposite  side,  with  the  exception  of  those  from  the  auditory. 
These  fibers  form  the  central  sensory  tracts  for  the  cranial  nerves 
from  whose  end  nuclei  they  originate. 


CHAPTER  X. 

GENERAL  ANATOMY  OF  THE  INTERIOR  OF  THE 
CEREBRAL  HEMISPHERES. 

Horizontal  or  sagittal  sections  through  a  cerebral  hemisphere 
show  it  to  be  made  up  entirely  of  gray  and  white  matter,  the 
former  completely  surrounding  the  latter,  forming  for  it  a  con- 
voluted mantle  of  a  thickness  nearly  uniform.  The  white  mat- 
ter appears  as  a  homogeneous  white  mass,  presenting  an 
irregularly  oblong  or  oval  shape,  and  is  called,  for  each  hemi- 
sphere, the  centrum  semiovale  (Vieussens).  The  white  matter, 
as  seen  on  complete  horizontal  section  of  the  entire  cerebrum, 
is  called  the  centrum  ovale  major.  Sections  of  the  centrum 
ovale  present  a  number  of  small  hemorrhagic  points,  which  are 
the  cross-sections  of  small  blood-vessels.  These  points  are 
called  the  puncta  vasculosa  (Fig.  190). 


CORPUS  CALLOSUM. 

On  separating  the  hemispheres,  a  broad  band  of  transversely 
arranged  fibers  appears  at  the  bottom  of  the  longitudinal  fissure. 
This  is  the  corpus  callosum,  or  the  great  transverse  commissure 
of  the  cerebrum,  connecting  corresponding  areas  of  the  frontal, 
parietal,  -and  occipital  lobes.  It  is  narrower  in  front  than  be- 
hind, is  7  to  8  cm.  (about  3^  inches)  in  length  on  its  superior 
surface,  and  is  from  5  to  6  cm.  (about  2^^  inches)  on  its  inferior 
surface,  and  extends  farther  forward  than  backward,  reaching  to 
a  point  within  3  cm.  (i^  inches)  of  the  anterior,  and  within 
5  cm.  (2  inches)  of  the  posterior  end  of  the  hemispheres.  It 
presents  a  gentle  curve  from  before  backward,  its  upper  surface 
being  convex,  its  lower,  concave.     Both  ends  are  more  thick- 

387 


388  CENTRAL  NERVOUS  SYSTEM. 

ened  than  the  intermediate  portion,  or  body.  The  posterior 
extremity  terminates  free,  and  is  rolled  upon  itself,  forming  an 
expanded  portion  called  the  spleniiim.  or  pad.  The  anterior 
extremity  curves  downward  and  backward  between  the  frontal 
lobes,  making;  a  bend  called  the  genu,  or  knee.     It  then  con- 


FiG.  190.— Horizontal  Section  of  Cerebrim  above  the  Corpus  Callosum  to  show 
THE  Cenirum  Ovale. — {After  Van  Gehiuhlen.) 

tinues  downward  and  backward,  and  at  the  base  of  the  brain  it 
blends  with  the  lamina  cinerea.  This  latter  portion,  the  re- 
flected part,  is  called  the  rostrum. 

Two  distinct  white  bands  are  given  off  at  the  termination  of 
the  corpus  callosum.  and  are  called  its  peduncles,  one  for  each 
side.     These  peduncles  diverge,  pass  across  the  posterior  por- 


ANATOMY   OF   INTERIOR   OF   CEREBRAL   HEMISPHERES. 


389 


tion  of  the  anterior  perforated  space,  and  enter,  each  on  its  own 
side,  the  fossa  of  Sylvius.  Thence  they  pass  to  the  apices  of 
the  temporal  lobes,  where  they  terminate,  possibly  uniting  with 
the  inner  olfactory  roots. 

On  the  upper  surface  of  the  corpus  callosum  are  a  number  of 
minute  transverse  depressions,  which  indicate  the  course  taken 
by  most  of  its  component  fibers.  A  longitudinal  furrow  exists 
in  the  middle,  and  has  on  each  side  two  small,  white  bundles  of 


fbr.Mon. 
cpt.  luc.  \ 

\ 


jornix 


fas 
pineal  atria, 
post    comm 
incal  bodi 


monhcala9 


nfiimxio 
pit  todu 

corp  alt 


tab.ualu 


Fig.  191. — Portion  of  a  Median  Section  of  the  Brain.     Showing  the  corpus  callosum, 
third  ventricle,  aqueduct  of  Sylvius,  fourth  ventricle,  pons,  cerebellum,  etc. 


fibers — the  nerves  of  Lancisi.  They  are  continuous  anteriorly 
with  the  peduncles  of  the  corpus  callosum.  Laterally,  near  the 
margins,  are  seen  other  fibers  having  a  longitudinal  course, 
called  the  striae  longitudinales  laterales.  Both  the  median  and 
lateral  striae  pass  backward  into  the  dentate  gyrus.  The 
median  portion  of  the  under  surface  of  the  corpus  callosum  is 
connected  in  front  with  the  septum  lucidum,  and  behind  with 
the  fornix.  The  transverse  fibers  of  the  corpus  callosum  are 
continuous  with  the  white  fibers  of  the  centrum  ovale,  and  inter- 


390 


CENTRAL  NERVOUS  SYSTEM. 


lace  with  the  various  projection  systems  of  fibers  and  continue 
to  the  cortex  of  each  hemisphere.  The  main  mass  of  the  trans- 
verse fibers  was  formerly  called  the  tapetum.  The  term  tape- 
turn  is  now  applied  to  the  association  bundle  of  fibers  described 


Fig.  192. — View  of  the  Corpus  Cali.osum  from  Above. — {Fro?ii  Sappey  after  FovilU, 

from  Qitain. ) 

The  upper  surface  of  the  corpus  callosum  has  been  fully  exposed  by  separating  the  cerebral 
hemispheres  and  throwing  them  to  the  side.  The  gyrus  fornicatus  has  been  partly  detached 
and  the  transverse  fibers  of  the  corpus  callosum  traced  for  some  distance  into  the  cerebral 
medullary  substance. 

I.  The  upper  surface  of  the  corpus  callosum.  2.  Median  furrow  or  raphe.  3.  Longitudinal 
striffi  bounding  the  furrow.  4.  Swelling  formed  by  the  transverse  bands  as  they  pass  into 
the  cerebrum,  arching  over  the  side  of  the  lateral  ventricle.  5.  Anterior  extremity  or  knee 
of  the  corpus  callosum.  6.  Posterior  extremity.  7.  Anterior,  and  8,  posterior,  fibers  pro- 
ceeding from  the  corpus  callosum  into  the  frontal  and  occipital  lobes  respectively.  9. 
Margin  of  the  swelling.  10.  Anterior  part  of  the  gyrus  fornicatus.  II.  Fissure  between 
the  corpus  callosum  and  this  convolution  opened  out.  Outside  12,  is  the  termination  of  the 
callosomarginal  fissure,  and  before  13  is  the  parieto-occipital  fissure.  13.  Upper  surface  of 
the  cerebellum. 


by  Forel  and  Onufrowicz,  The  fibers  of  the  corpus  callosum, 
which  pass  forward  into  the  frontal  lobes,  above  the  anterior 
cornu  on  each  side,  are  termed  the  forceps  minor ;  while  those 
that  come  from  the  splenium,  and  curve  backward  into  the 
occipital  lobes,  above  the  posterior  cornua,  are  called  the  forceps 


Fig.  193. — Photograph  of  Horizontal  Section  through  Cerebrum  to  Show 
Lateral  Ventricles. 
S.L.F.  Superior  longitudinal  fissure.  C.O.M.  Centrum  ovale  minor.  F.M.  Foramen  ol 
Monro.  A.P.F.  Anterior  pillar  of  fornix.  F.  Body  of  fornix.  D.P.F.  Descending  or 
posterior  pillar  of  fornix.  P.I.N.  Posterior  incised  cerebellar  notch.  C.C.  Corpus 
callosum.  P.C.L.  Posterior  cornu  of  lateral  ventricle.  Em.C.  Eminence  due  to  calcarine 
fissure  called  calcar  avis  or  hippocampus  minor.  H.M.  Hippocampus  major.  D.C.L. 
Descending  cornu  of  lateral  ventricle.  F.  F.  Corpus  fimbriatum.  C.P.L.  Choroid  plexus 
of  lateral  ventricle.  O.T.  Optic  thalamus.  T.C.N.  Tail  of  caudate  nucleus.  T.S. 
Taenia  semicircularis.  V.C. ST  Vena  corpora  striata.  S.S.  Sulcus  semilunaris.  H.C.N. 
Head  of  caudate  nucleus.  A.C.L.  Anterior  cornu  of  lateral  ventricle.  S.L.  Septum 
lucidum. 

391 


ANATOMY   OF   INTERIOR   OF   CEREBRAL   HEMISPHERES.  393 

major.  The  median  surfaces  of  the  hemispheres,  which  overlap 
the  corpus  callosum,  are  called  the  labia  cerebri.  The  space 
between  them  and  the  superior  surface  of  the  corpus  callosum 
is  frequently  called  the  ventricle  of  the  corpus  callosum. 


THE  LATERAL  VENTRICLES. 

In  order  to  expose  the  lateral  ventricles,  a  horizontal  section 
through  the  cerebrum  should  be  made  at  a  level  with  the  corpus 
callosum,  and  then  a  longitudinal  incision  should  be  made  through 
the  corpus  callosum  on  each  side  of  its  middle  line  or  raphe,  when 
the  ventricular  cavities  will  be  exposed,  the  corpus  callosum  form- 
ing their  roof.  The  lateral  ventricles  are  the  cavities  of  the  second- 
ary fore-brain  and  belong  entirely  to  the  hemispheres.  They 
are  situated  deep  in  the  centrum  ovale,  and  do  not  communicate 
with  each  other,  but  communicate  with  the  cavity  of  the  primary 
fore-brain,  the  third  ventricle,  by  an  opening  on  each  side,  the 
foramen  of  Monro,  which  is  the  remains  of  a  much  larger  pas- 
sage, communicating  in  the  fetus  with  the  primary  and  the  second- 
ary fore-brain.  The  ventricular  cavities  are  lined  with  ciliated 
epithelium  of  the  columnar  variety,  which  rests  on  a  neuroglia 
basis — the  ependyma.  They  contain  normally  a  small  amount  of 
serum.  Each  ventricle  consists  of  a  middle  portion  or  body 
with  three  extensions  or  cornua  :  the  anterior,  the  middle,  often 
called  the  lateral,  or  descending  cornu,  and  the  posterior  cornu. 
The  body  of  the  ventricle  lies  between  the  foramen  of  Monro  and 
the  posterior  extremity  of  the  corpus  callosum.  Internally  it  is 
separated  from  its  fellow  by  a  thin  blade  of  white  matter,  the 
septum  lucidum,  which  septum  is  connected  above  with  the  under 
surface  of  the  corpus  callosum  and  below  with  the  fornix.  The 
ventricle  has  for  its  floor,  from  before  backward,  the  intraven- 
tricular portion  of  the  corpus  striatum,  or  caudate  nucleus,  the 
taenia  semicircularis,  the  optic  thalamus,  the  choroid  plexus,  and 
one-half  of  the  body  of  the  fornix.  The  anterior  cornu  curves 
around  the  anterior  extremity  of  the  corpus  striatum  to  reach 
the  frontal  lobe.  It  has  for  its  front  wall  and  roof  the  corpus 
callosum.  On  the  inner  side  is  the  septum  lucidum.  On  the 
outer  side  is  the  head  of  the  caudate  nucleus.     The  middle  or 


394  CENTRAL  NERVOUS  SYSTEM. 

descending-  cornii  is  the  largest  and  longrest  of  the  three.  It 
passes  at  first  backward  and  outward,  then  downward  and  for- 
ward, forming  in  its  course  a  great  curve  around  the  back  of  the 
optic  thalamus  and  crus  cerebri.  It  then  proceeds  forward  and 
inward  to  terminate  near  the  apex  of  the  temporal  lobe  close  to 
the  amygdalum.  This  cornu  is  roofed  by  the  body  of  the  corpus 
callosum  and  tapetum,  and  has  prolonged  into  it  the  caudate 
nucleus,  the  corpus  striatum,  the  taenia  semicircularis,  and  a  small 
part  of  the  optic  thalamus.  It  has  for  its  floor  the  hippocampus 
major,  or  cornu  ammonis,  the  pes  hippocampus,  the  eminentia 
collateralis,  and  the  fimbria  of  the  fornix.  The  hippocampus 
major,  or  cornu  ammonis, — so  called  because  of  its  resemblance 
to  a  ram's  horn. — is  a  curved  eminence  extending  along  the  entire 
lenordi  of  the  floor  of  the  descending  horn.  It  is  the  ventricular 
portion  of  the  gyrus  hippocampus,  and  is  due  to  the  extension 
inward  of  the  dentate  or  hippocampal  sulcus  of  the  mesial  sur- 
face of  the  temporal  lobe,  the  gray  matter  of  which  is  separated 
from  the  cornu  ammonis  by  a  thin  layer  of  white  matter  covered 
by  ependymal  tissue,  called  the  alveus.  This  cornu,  as  it 
descends  and  approaches  its  termination,  becomes  enlarged  and 
presents  along  its  edges  a  number  of  digitations,  which,  from 
their  resemblance  to  the  paw  of  an  animal,  give  it  the  name 
pes  hippocampus. 


EMINENTIA  COLLATERALIS. 

This  is  a  white  eminence  between  the  cornu  ammonis  and  the 
outer  wall  of  the  descending  horn  of  the  lateral  ventricle,  and  is 
due  to  the  extension  inward  of  the  collateral  fissure.  The  tri- 
gonum  ventriculi  is  the  space  between  the  eminentia  collateralis 
and  the  cornu  ammonis. 

The  fimbria,  often  called  the  corpus  fimbriatum,  is  the  pro- 
longed posterior  pillar  of  the  fornix,  which  extends  into  the  de- 
scending cornu,  and  can  be  traced  forward  to  the  uncinate 
gyrus.  It  is  attached  by  its  inner  margin  to  the  hippocampus 
major,  while  its  outer  border  is  free,  and  lies  on  the  upper  sur- 
face of  the  hippocampus. 

The  posterior   cornu   begins  at  the  splenium   of  the  corpus 


-1-  ^ 


f 

J.M. 
c.c. 

th.opt. 

pi.ch. 

T. 


/.ma. 


""•-ii 


Fig.  194. — View  from  Above  and  the  Side  of  the  Whole  Left  Lateral  Ventricle. 
Natural  size. — [E.  A.  S.  and  G.  D.  T.,from  Quain.) 

The  insula  has  been  sliced  away  and  the  middle  or  descending  cornu,  c.i.,  exposed.  Within 
this  are  seen  the  following  parts  :  c.i.  Entrance  to  cornu  inferius.  h.  The  hippocampus 
major,  coll.  The  eminentia  collaieralis.  fi.  Fimbria,  continued  from  the  fornix,  tri. 
Trigonum  ventriculi.  calcar.  Calcar  avis.  c.p.  Cornu  posterius.  c.a.  Cornu  anterius 
of  ventricle,  f.  Fornix.  /''.  Its  anterior  pillar,  f.  M.  Foramen  Monroi.  c.c.  Corpus 
callosum.  th.opt.  Thalamus  opticus,  anterior  tubercle,  pi ch.  Plexus  choroides.  f.ma. 
Forceps  major. 

395 


ANATOMY   OF   INTERIOR   OF   CEREBRAL   HEMISPHERES. 


397 


callosum  and  curves  backward  and  inward  into  the  occipital  lobe. 
It  has  for  its  upper  and  outer  walls  the  tapetum.  Its  inner  and 
lower  walls  have  three  projections.  The  upper  is  the  marginal 
bundle  of  fibers  of  the  corpus  callosum,  called  the  forceps  pos- 
terioris.  The  middle  projection  is  due  to  the  calcarine  fissure, 
which  extends  deep  into  the  margin  of  the  hemisphere  and 
pushes  before  it  the  wall  of  this  cornu,  producing  an  eminence 


Fig.  195.— Two  Views  of  a  Plaster  Cast  of  the  Cavities  of  the  Cerebral  Ven- 
tricles.— {After  Welcker,  from  Qiiaiii.) 

A.  From  above:  I.  Nucleus  caudatus.  2.  Middle  cornu.  3.  Fourth  ventricle.  4.  Calcar 
avis.  5.  Third  ventricle.  6.  Middle  or  soft  commissure.  7.  Sylvian  aqueduct.  8.  Re- 
cessus  lateralis.  B.  From  the  side:  I.  Nucleus  caudatus.  2.  Middle  commissure.  3. 
Optic  thalamus.  4.  Recessus  suprapinealis.  5.  Recessus  pinealis.  6.  Aqueduct  of  Syl- 
vius. 7.  Posterior  cornu.  8.  Fourth  ventricle.  9.  Recessus  lateralis.  10.  Middle  or 
descending  cornu.  II.  Chiasm.  12.  Anterior  commissure.  13.  Anterior  cornu.  The 
projections  into  the  cavities  of  the  structures  which  bound  the  ventricles  are  seen  as  impres- 
sions upon  the  cast. 


called  the  hippocampus  minor,  or  calcar  avis.  The  lowermost 
projection  is  a  thickening  due  to  a  bundle  of  white  fibers — the 
inferior  longitudinal  fasciculus. 

The  floor  of  the  body  of  the  lateral  ventricle  contains  the  fol- 
lowing bodies  :  the  corpus  striatum,  the  taenia  semicircularis, 
the  optic  thalamus,  and  the  choroid  plexus.  The  latter  will  be 
described  later. 


398 


CENIRAL  NERVOUS  SYSTEM. 


THE  CORPORA  STRIATA. 


The  corpora  striata,  tooether  with  the  claustral  and  amygda- 
loid nuclei,  are  the  ganglia  of  the  cerebral  hemispheres.  The 
corpora  striata  are  situated  deep  in  the  cerebral  hemispheres, 
ventrolateral  to   the   optic  thalami,  being   separated   from    the 


Fig.  196. — Photoorai'H  of  a  Section  through  the  Frontal  and  Tip  of  Temporal 

I.OBES. 

S.I.F.  Superior  longitudinal  fissure.  C.C.  Corpus  callosum.  A.P.F.  Anterior  pillar  of  fornix. 
S.F.G.  Superior  frontal  gyrus.  L.V.  Lateral  ventricle.  H.C.N.  Head  of  caudate  nu- 
cleus. I.e.  Internal  capsule.  M.F.G.  Middle  frontal  gyrus.  F.C.  External  capsule. 
L.N.  Lenticular  nucleus.  I.F.G.  Inferior  frontal  gyrus.  A.C.  Anterior  commissure. 
T. L.  Temporal  lobe.     O.N.   Optic  nerve. 


latter  bodies  by  the  taenia  semicircularis,  or  striae  corneae.  They 
are  so  named  because  of  their  streaked  appearance  on  trans- 
verse section,  this  appearance  being  due  to  the  passage  through 
them  of  the  fasciculi  of  white  fibers  which  compose  the  internal 
capsule.     Each   corpus  may  be  described  as  an   oval   mass  of 


ANATOMY   OF   INTERIOR   OF   CEREBRAL   HEMISPHERES.  399 

gray  and  white  matter,  located  deep  in  the  hemisphere,  and  con- 
sists of  two  parts — an  extraventricular,  or  nucleus  lenticularis, 
which  is  entirely  embedded  in  the  white  matter,  and  an  intra- 
ventricular portion,  or  caudate  nucleus,  which  is  within  the 
lateral  ventricle.  This  division  of  each  corpus  striatum  is  due 
to  bundles  of  fibers  from  all  parts  of  the  cerebral  cortex,  which, 
converging,  pass  through  this  ganglion  on  their  way  to  the  crus 
cerebri.  These  fibers  do  not  produce  a  complete  separation  of 
the  lenticular  from  the  caudate  nucleus,  as  they  are  united  an- 
teriorly and  posteriorly  by  slender  tracts  of  fibers.  The  extra- 
ventricular  or  lenticular  nucleus  is  bounded  internally  by  the 
internal  capsule,  externally  by  the  external  capsule,  which  sepa- 
rates it  from  the  claustrum,  a  thin  layer  of  gray  matter  with  a 
wavy  margin.  Inferiorly,  it  is  bounded  by  the  lenticular  loop. 
Its  horizontal  section  has  the  shape  of  a  double  convex  lens  ; 
hence  its  name.  On  vertical  section  it  is  triangular  in  shape. 
It  is  separated  into  three  zones  by  two  laminse  of  white  fibers 
from  the  internal  capsule,  and  by  axones  of  its  own  cells  on 
their  way  to  the  lenticular  loop.  The  outer  or  larger  part  is 
called  the  putamen ;  the  inner  two  zones,  from  their  pale  color, 
are  called  the  globus  pallidus.  The  intraventricular  or  caudate 
nucleus  is  pyriform  in  shape,  and  consists  of  an  anterior  ex- 
panded portion,  or  head,  and  a  narrow-  posterior  portion,  or 
tail.  The  head  forms  the  outer  wall  and  part  of  the  floor  of  the 
anterior  cornu.  The  tail  extends  backward  alone  the  outer 
part  of  the  floor  of  the  lateral  ventricle,  then  passes  downward 
and  forward  into  the  descending  cornu,  terminating  near  its 
end  in  the  amygdaloid  nucleus  or  tubercle.  It  is  covered  by 
ependymal  tissue,  upon  which  rests  the  ciliated  epithelium  com- 
mon to  the  ventricles.  On  its  outer  side  is  the  internal  capsule, 
which  separates  it  from  the  lenticular  nucleus.  The  caudate 
nucleus,  with  the  optic  thalamus,  forms  the  inner  boundary  of 
the  internal  capsule.  The  two  nuclei  are  continuous  anteriorly 
with  each  other  by  small  bands  of  gray  matter  in  the  ventral 
portion  of  the  anterior  limb  of  the  capsule.  The  head  of  the 
caudate  nucleus  is  continuous  inferiorly  with  the  anterior  per- 
forated space,  which,  In  turn,  is  also  connected  with  the  anterior 
inferior  extremity  of  the  lenticular  nucleus.     Through  the  ventral 


400 


CENTRAL  NERVOUS  SYSTEM. 


and  basal  portion  of  the  lenticular  and  caudate  nuclei  passes  a 
compact  bundle  of  fibers — 'the  anterior  commissure.  From  the 
posterior  end  of  the  putamen,  or  the  outer  division  of  the  lentic- 
ular nucleus,  passes  a  process  of  gray  matter  into  the  roof  of 
the  descending-  horn  of  the  lateral  ventricle,  which  joins  the  tail 
of  the  caudate  nucleus,  thus  uniting  these  two  nuclei  posteriorly. 
Microscopic  examination  of  these  two  nuclei  shows  that  they 
contain  two  chief  forms  of  multipolar  cells — large  rectangular  and 


Fig.  197. — Photograph  ok  Sagittal  (Longitudinal)    Section  through  a  Cererral 

Hemisphere, 

C.O.F.  Centrum  ovale  of  frontal  lobe.  C.R.  Corona  radiata.  C.O.P.  Centrum  ovale  of 
parietal  lobe.  C.O.O.  Centrum  ovale  of  occipital  lobe.  D.ILL.  Descending  or  middle 
horn  of  lateral  ventricle.  C.A.  Cornu  ammonis.  N.L.  Nucleus  lenticularis.  C.O.T. 
Centrum  ovale  of  temporal  lobe. 


small  triangular,  polygonal,  or  spindle-shaped  cells.  The  former 
are  found,  according  to  Koelliker,  almost  exclusively  in  the 
putamen,  while  the  smaller  cells  are  found  throughout  the  globus 
pallidus  and  the  caudate  nucleus.  According  to  Starr,  both  vari- 
eties are  scattered  indifferently  throughout  the  gray  matter,  and 
are  never  associated  into  groups.  The  large  cells  have  a  slen- 
der body,  from  36  to  70  f.i  long,  and  give  off  from  each  end  one 
or  two,   occasionally   three   to   five,  very   long  dendrites,  which 


ANATOMY   OF   INTERIOR   OF   CEREBRAL   HEMISPHERES. 


401 


soon  turn,  nearly  at  right  angles  to  the  long  axis  of  the  cell-body. 
They  have  a  very  long  course,  and  do  not  branch  more  than 
twice.  Just  prior  to  reaching  their  destination  they  fork.  The 
axones  come  off  either  from  a  projection  from  the  cell-body  or 


Fig.  198. — MicROPHOTOGRAPH  OF  Large  Rectangular  Cells  of  Corpora  Striati. 
Golgi  method. — [J/ter  Stai-i'. ) 


from  the  base  of  one  of  the  dendrites.  The  cells  of  the  globus 
pallidus  and  of  the  nucleus  caudatus  are  practically  the  same  in 
appearance,  save  that  in  the  former  they  are  smaller.  They  are 
from  20  to  40  li  in  diameter,  possessing,  from  all  sides  of  the 
cell-body,  many  branching  dendritic  processes  studded  with 
26 


402  CENTRAL  NERVOUS  SYSTEM. 

gemmules.  The  axones  come  from  the  cell-body,  but  their 
course  is  ditticult  to  trace.  Those  from  the  large  cells  of  the 
putamen  pass  either  through  the  globus  pallidus  and  enter  the 
internal  capsule  to  pass  into  the  crus  cerebri,  or  the  greater 
number  may  pass  by  way  of  the  lenticular  loop  (ansa  lenticu- 
laris),  to  be  described. 


THE    LENTICULAR    LOOP,    OR    ANSA    LENTICULARIS. 

The  lenticular  loop  is  a  rather  large  fasciculus  of  fibers  which 

proceeds  from  the  medullary  laminae  between  the  divisions  ot 


0  P.     T  H . 


^^  m 


Fig.  199. — Diagram  ok  a  Section  through  the  Crus,  ktc.  in  Front  ok  the 
CoRi'ORA  QUADRIGEMINA. — {^Modified froiH  Wernicke.) 
P  C.   Posterior    commissure.      Aq.    Aqueduct   of   Sylvius.      P  L.    Posterior   longitudinal   fibers 
III.  Third  nerve.     L  B.  Luys' body.    OP  T.  Optic  tract.    O.  P.  T.H.  Optic  thalamus.  Int. 
Cap.  Internal  capsule.    Lent.  Loop.  Lenticular  loop.      R.N.  Red  nucleus.  Lent.  N.  Lentic- 
ular nucleus. 

the  lenticular  nucleus.  These  fibers  have  their  origin  chiefly  from 
the  cells  of  the  outer  division  of  the  lenticular  nucleus  (the  puta- 
men). and,  according  to  some  observers,  the  loop  receives  acces- 
sions of  fibers  from  the  caudate  nucleus  and  the  cerebral  cortex. 
This  tract  courses  mesially  beneath  the  globus  pallidus.  from 
w^hich  point  the  course  and  termination  of  its  component  fibers 
is  much  in  dispute. 

Von    Monakow    believes    that    the    fibers    of   this    tract    are 
arranged  into  three  disdnct  bundles — two  anterior  and  one  pos- 


ANATOMY   OF   INTERIOR   OF   CEREBRAL    HEMISPHERES.  403 

terior.  The  two  anterior  bundles  pierce  the  internal  capsule 
and  crus  cerebri  in  curves  at  the  level  of  Luys'  body,  both  bun- 
dles passing-  into  that  body ;  the  most  ventral  bundle  passes 
into  the  ventral  surface  of  the  body,  terminating  about  its  nerve- 
cells,  while  most  of  the  fibers  of  the  more  dorsally  placed  bundle 
pass  into  the  body  through  its  dorsal  portion  ;'  the  remaining  fibers 
unite  with  fibers  of  an  unknown  origin  to  pass  forward  and  in- 
ward to  the  region  of  the  tuber  cinereum,  where  they  terminate. 

The  posterior  bundle — the  largest  of  the  three,  and  the  one 
commonly  called  the  lenticular  loop — does  not  pierce  the  crus 
cerebri,  but  courses  between  the  crus  cerebri  and  the  anterior 
pillar  of  the  fornix,  and  then  curves  upward  and  inward  to  end 
in  the  gray  matter  beneath  the  ependyma  of  the  third  ventricle 
and  in  the  optic  thalamus. 

According  to  von  Bechterew,  the  lenticular  loop  also  contains 
centripetally  coursing  fibers  from  the  mesial  fillet  or  lemniscus. 
These  fibers  are  the  axones  from  the  cells  of  the  nucleus  cune- 
atus  of  the  opposite  side.  They  probably  terminate  about  the 
cells  of  the  globus  pallidus.  From  these  cells  new  fibers  start 
out  and  pass  upward  through  the  centrum  semiovale  to  arborize 
about  the  cells  of  the  cortex  of  the  central  and  parietal  lobes. 
These  cortical  (sensory)  neurones  probably  form  the  tegmental 
radiation  of  Edinger. 

The  axones  from  the  cells  of  the  caudate  nucleus  pass  into 
the  internal  capsule  ;  thence  downward  toward  the  base  of  the 
brain,  where  they  curve  backward  to  enter  the  optic  thalamus 
and  adjacent  nuclei.  A  few  axones  from  the  cells  of  the  cau- 
date nucleus  pass  dorsolaterally  through  the  internal  capsule 
and  globus  pallidus  to  enter  the  lenticular  loop. 


THE  TRACTUS  STRIOTHALAMICUS  (Edinger). 

Edinger  has  discovered  a  tract  of  fibers  which  exists  in  all 
vertebrates,  and  takes  its  origin  from  the  cells  of  the  head  of 
the  caudate  nucleus  and  from  those  of  the  putamen.  These 
fibers  form  a  distinct  bundle,  which  passes  downward  through  the 
anterior  limb  of  the  internal  capsule  to  the  base  of  the  brain, 
whence  they  curve  dorsally  to  reach  the  optic  thalamus,  where 


404  CENTRAL   NERVOUS  SYSTEM. 

most  of  them  terminate  ;  a  few  fibers,  however,  continue  back- 
ward beneath  the  optic  thalamus  and  end  in  the  posterior  corpus 
quadrigeminum  and  in  the  substantia  nigra  (Fig.  200). 


THE  TJENIA  SEMICIRCULARIS. 

The  taenia,  also  called  stria  cornea:^  and  stria  terminalis,  is  a 
fasciculus  of  white  fibers  which  forms  the  boundary  between 
the  nucleus  caudatus  of  the  corpus  striatum  and  the  optic  thal- 
amus. It  is  placed  superficially  in  the  side  of  a  depression — the 
sulcus    semilunaris — between   the   nucleus    caudatus    and  optic 


Fig.  200. — Scheme  Showing  the  Tkactus  Striothalamicus. — [After  Ediuger.) 

thalamus.  Beneath  this  bundle,  occupying  the  bottom  of  the 
depression,  is  the  vena  corporis  striati,  which  receives  a  number 
of  superficial  veins  from  the  corpus  striatum  and  optic  thalamus 
and  joins  the  vena  Galeni.  Ihe  anterior  portion  ot  the  taenia 
descends,  in  front,  between  the  anterior  extremity  of  the  opdc 
thalamus  and  head  of  the  caudate  nucleus.  Some  of  its  fibers 
join  the  anterior  commissure,  and  the  remainder  continue  to  the 
base  of  the  brain  and  terminate  in  the  gray  matter  of  the  ante- 
rior perforated  space.  Schwalbe,  however,  states  that  the 
taenia  divides  into  two  parts  anteriorly,  one  of  which  is  con- 
tinuous with  the  anterior  pillar  of  the  fornix  ;  the  other  passes 
in  front  of  the  anterior  commissure,  to  become  lost  in  the  gray 


Fig.  201. — Photograph   of   a  Longitudinal    Section    through  a  Cerebral  Hemi- 
sphere TO  SHOW  the  Ganglia  of  the  Hemisphere. 
S.F.G.   Superior  frontal  gyrus.     M.F.G.   Middle  frontal  gyrus.     I.F.G.  Inferior  frontal  gyrus. 
Ex.C.   External  capsule.     Cls.    Claustrum.     I.R.   Insula  or  island  of  Reil.    N.A.   Nucleus 
amygdala.      G.P.    Globus  pallidus  of  lenticular  nucleus.     Int.C.   Interna]  capsule.      C.N. 
Caudate  nucleus. 

405 


ANATOMY    OF   INTERIOR   OF    CEREBRAL    HEMISPHERES.  407 

matter  between  the  septum  lucidum  and  head  of  the  caudate 
nucleus.  Posteriorly,  it  passes,  in  conjunction  with  the  tail  ot 
the  caudate  nucleus,  into  the  descending  cornu  of  the  lateral 
ventricle,  both  terminating  in  the  nucleus  amygdala.  The 
nucleus  amygdala  is  a  thickening  of  the  cortex  near  the  apex 
of  the  temporal  lobe,  producing  a  bulging  in  the  roof  of  the  de- 
scending cornu  called  the  amygdaloid  tubercle.  It  is  dorsal  to 
the  nucleus  lenticularis,  with  which  it  is  probably  continuous. 
The  claustrum  is  a  thin,  wavy  sheet  of  gray  matter,  having  on 
its  inner  side  a  narrow  strip  of  white  matter — the  external  cap- 
sule— and  on  its  outer  side  the  cortex  of  the  insula  or  island  of 
Reil.  Anteriorly,  it  blends  with  the  nucleus  amygdala  (Ober- 
steiner). 

THE  INTERNAL  CAPSULE. 

This  receives  its  name  because  it  bounds  the  lenticular 
nucleus  internally,  and  is  one  of  the  most  important  parts, 
anatomically,  of  the  whole  nervous  system.  It  is  composed  of 
a  number  of  important  tracts  of  medullated  nerve-fibers,  whose 
function  is  to  brine  the  cerebral  cortex  into  anatomic  and 
physiologic  relation  with  parts  below — namely,  the  pons,  cere- 
bellum, medulla,  and  spinal  cord.  Hence,  it  must  contain  both 
centripetal  and  centrifugal  tracts  of  fibers.  The  clearest  type 
of  its  topography  can  be  obtained  from  horizontal  sections 
through  the  hemisphere  and  basal  ganglia.  It  is  a  broad,  homo- 
geneous band  of  white  matter  (fasciculi  cut  across)  between 
the  lenticular  nucleus  on  its  outer  and  the  caudate  nucleus  and 
optic  thalamus  on  its  inner  side.  It  consists  of  two  divisions 
or  limbs, — an  anterior  and  a  posterior, — united  with  each  other 
at  an  angle,  which  is  called  the  knee  or  elbow  of  the  capsule. 
The  anterior  portion  or  limb,  which  is  the  shorter,  is  between 
the  lenticular  nucleus  on  the  outer  side  and  the  caudate 
nucleus  on  the  inner  side  ;  and  the  posterior  portion  or  limb 
is  between  the  lenticular  nucleus  on  the  outside  and  the  optic 
thalamus  on  the  inside.  Anteriorly,  posteriorly,  and  superiorly 
it  blends  with  the  centrum  semiovale.  The  fibers  of  which  it  is 
composed  radiate  fan-shaped  toward  all  parts  of  the  cortex, 
forming  the  corona  radiata  of  Reil.     Below,  the  internal  capsule 


4o8  CENTRAL  NERVOUS  SYSTEM. 

is  continuous  with  the  crus  cerebri.  Experiments  on  animals, 
and  clinical  observations  verified  by  pathologic  researches  in 
man,  prove  that  the  anterior  limb  of  the  capsule  is  composed  of 
a  tract  of  projection  fibers  going  to  the  optic  thalamus  and  of  a 
tract  of  fibers  connecting  that  portion  of  the  frontal  lobes  which 
is  in  front  of  the  central  convolutions  (the  prefrontal  lobe)  with 
the  opposite  cerebellar  hemisphere.  This  is  the  frontocerebellar 
tract.  In  the  anterior  two-thirds  of  the  posterior  limb  is  the 
great  motor  tract;  the  posterior  third  contains  the  tracts  which 
convey  touch,  temperature,  and  muscle  sense,  as  well  as  the 
optic  and  auditory  tracts,  and  a  tract  of  projection  fibers  con- 
necting the  temporal  and  occipital  lobes  with  the  opposite  cere- 
bellar hemisphere.  Apart  from  the  above-mentioned  systems  of 
fibers,  the  capsule  contains,  in  addition,  projection  fibers  which 
unite  all  parts  of  the  cerebral  cortex  with  each  optic  thalamus. 

The  exact  locadon  of  the  different  tracts  of  which  the  internal 
capsule  is  composed  is  as  follow^s:  In  the  anterior  limb  are  two 
tracts  of  fibers,  the  ventral  of  which  is  a  projection  bundle  of 
fibers  to  the  optic  thalamus  from  the  frontal  lobe.  It  is  of  no 
great  clinical  importance.  The  dorsal  bundle  is  a  large  fascicu- 
lus (frontocerebellar)  collecdng  its  fibers  from  all  parts  of  the 
frontal  lobe,  and  thence  passing  to  the  opposite  cerebellar  hemi- 
sphere via  the  nucleus  pontis,  a  few  fibers  being  connected  with 
the  cerebellar  hemisphere  of  the  same  side. 

The  posterior  limb  contains  the  motor  and  sensory  tracts. 
The  motor  tract,  which  occupies  the  anterior  two-thirds  of  this 
limb,  may  be  divided  into  the  following  fasciculi  of  fibers,  enu- 
merated from  before  backward  :  The  most  anterior  bundle  is 
made  up  of  fibers  conveying  motor  impulses  to  the  facial  mus- 
cles ;  it  is  located  just  ventral  to  the  knee  of  the  capsule. 
Posterior  to  the  facial  fibers,  fibers  come  from  before  backward — 
the  motor  fibers  to  the  hypoglossal  nerve,  to  the  arm,  the  leg, 
and  the  trunk,  in  regular  order,  as  indicated  by  the  diagram 
(Fig.  203). 

Just  dorsal  to  the  motor  or  pyramidal  part,  occupying  the 
posterior  third  of  the  capsule,  is  the  sensory  tract.  The  extreme 
posterior  part  of  the  posterior  limb  of  the  capsule  contains  the 
opdc  and  auditory  tracts,  the  latter  being  external  to  the  former. 


Fig.  202. — Photograph  of  a  Horizontal  Section  through  a  Cerebral  Hemisphere 
TO  Relations  of  Internal  Capsule. 

O.T.  Optic  thalamus.  P.L.I. C.  Posterior  limb  of  internal  capsule.  K.I.C.  Knee  of  internal 
capsule.  A.L.I.C.  Anterior  limb  of  internal  capsule.  H.C.N.  Head  of  caudate  nucleus. 
Ex.C.  External  capsule.  L.N.  Lenticular  nucleus.  F.  S.  Fissure  of  Sylvius.  Ins. 
Insula.      Cls.   Claustrum. 

409 


facialis 


Ifi/poglossus 
■i-PhomtionsKcrn 


5ensor.BundsL-S. 
3ehstrahlung 


riic 

^cuslzcusbundd 


Fig.  203. — Horizontal  Section  through  the  Right  Hemisphere  of  a  Man. 
— [After  von  Moiiakow^) 
The  important  parts  of  the  internal  capsule  are  colored  red. 
B.Kn.   Knee   of    corpus   callosum.       Vh.  Anterior  horn  of  lateral  ventricle.     F\.   Inferior  o 
third  frontal  convolution.       /  stric.  lenticulostriate  division  of  internal  capsule.      Knie  if. 
Knee  of  internal  capsule.     I  optic.  Lenticulo-optic  division  of  internal  capsule.      77/.  Optic 
thalamus.    J.  Insular  island  of  Reil.     CI.  Claustrum.     Operc.   Operculum.     T^.  First  tem- 
poral convolution,     rlic.   Retrolenticular  region  of  internal  capsule.      CA.   Ammonis  horn. 
calc.   Calcarine  fissure.       Bh.   Posterior  horn  of   lateral  ventricle,     .tj-.   Optic  radiation  of 
Gratiolet.     7;.    Second  temporal  convolution.     777«V?/w.  Position  in  capsule  of  facial  bundle 
of  fibers.     Hypoglossus.   Position  of  hypoglossal  fibers.     Ar77i.   Position  of  arm  fibers.    Bein. 
Position  of  fibers   for  leg.     Sensor,  biindel.      Sensory   fibers.      Sehstrahhing.   Optic  tract. 
AcusticusbUndei.     Auditory  tract. 

411 


ANATOMY    OF    INTERIOR   OF    CEREBRAL    HEMISPHERES.  413 

In  addition  to  the  before-mentioned  tracts,  the  posterior  hmb  of 
the  capsule  contains  a  fasciculus  of  fibers  connecting  the  occip- 
ital and  temporal  lobes  with  the  opposite  cerebellar  hemisphere, 
as  well  as  projection  fibers  from  the  same  source  to  the  optic 
thalamus. 


THE    FORNIX. 

The  fornix  is  composed  of  longitudinally  arched  bundles  of 
fibers  consisting  of  symmetric  halves — one  for  each  hemisphere. 
It  has  a  body  and  two  pillars  or  columns  for  each  side,  one 
anterior  and  one  posterior.  It  is  located  beneath  the  corpus 
callosum,  with  which  it  is  continuous  behind,  being  separated 
from  it  in  front  by  the  septum  lucidum.  The  body  of  the  fornix 
rests  upon  the  velum  interpositum,  which  separates  it  from  the 
optic  thalamus  and  third  ventricle  below.  It  is  triangular  in 
shape  ;  broad  behind,  narrow  in  front.  Its  lateral  surfaces  form 
part  of  the  floor  of  the  body  of  each  lateral  ventricle.  The 
anterior  pillars,  or  columnae  fornicis,  are  two  roundish  bundles 
of  nerve-fibers  which  descend  through  the  gray  matter  of  the 
third  ventricle,  behind  the  anterior  commissure  and  in  front  of 
the  foramen  of  Monro  on  each  side,  forming  its  anterior  boun- 
dary. As  they  descend  they  diverge,  leaving  an  interval  which 
is  occupied  by  the  septum  lucidum.  They  receive  a  few  fibers 
from  the  taenia  semicircularis,  the  crura  of  the  pineal  gland,  and  the 
septum  lucidum.  According  to  Koelliker,  the  taeniae  semicir- 
cularis do  not  unite  with  these  pillars  ;  on  reaching  the  base 
of  the  brain  they  curve  backward  and  upward,  around  the  cor- 
pora albicantia,  forming  loops  which  make  the  white  portion,  or 
stratum  zonale,  of  these  bodies.  They  end  in  arborizations  about 
the  inner  cell-groups  of  these  bodies.  These  cell-groups  also 
have  terminating  about  them  a  fasciculus  of  fibers  (axones  from 
the  cells  of  the  ventral  nucleus  of  the  optic  thalamus)  which  is 
called  the  bundle  of  Vicq  d'Azyr,  or  fasciculus  thalamomam- 
millaris. 

The  posterior  pillars  of  the  fornix  are  two  flattened  bands — 
prolongations  from  the  sides  of  the  body  of  the  fornix.  At  their 
commencement  their  upper  surfaces  are  adherent  to  the  under 


414  CENTRAL  NERVOUS  SYSTEM. 

surface  ot  the  corpus  callosuni.  Between  these  diverging  crura 
and  the  splenium  of  the  corpus  callosum  exists  a  triangular  area 
of  white  matter,  the  psalterium,  which  presents  on  its  surface  a 
number  of  transverse  obhque  and  longitudinal  lines.  Prom 
the  fancied  resemblance  these  bear  to  the  strings  of  a  harp,  this 
area  is  also  called  the  lyra.  The  psalterium  is  a  commissure 
between  the  cornua  ammonis.  Each  crus  curves  downward  and 
outward  around  the  pulvinar  of  the  optic  thalamus,  then  enters 
the  descending  cornu  of  the  lateral  ventricle,  giving  off  some 
fibers  to  the  hippocampus  major,  w^iile  the  rest  continue  along 
the  inner  border  of  the  cornu  to  end  in  the  gyrus  hippocampus 
and  uncinate  gyrus.  The  latter  fibers  form  the  before-mentioned 
fimbria.  The  study  of  secondary  degenerations  proves  that  the 
fibers  of  the  fornix  really  proceed  from  the  cornu  ammonis  and 
region  of  the  gyrus  hippocampus  and  pass  to  the  corpus  mam- 
millare. 


THE    SEPTUM    LUCIDUM. 

The  septum  lucidum  forms  the  inner  boundary  of  the  lateral 
ventricles,  and  is  united  in  front  with  the  anterior  portion  (the 
genu)  and  the  descending  portion  (the  rostrum)  of  the  corpus  cal- 
losum. Posteriorly  and  inferiorly  it  unites  with  the  fornix  and  its 
anterior  peduncles.  It  is  a  triangular  area  of  white  matter,  con- 
sisting of  two  very  thin  laminae  separated  by  a  narrow  closed 
space  which  contains  a  little  fluid.  This  interval  or  space  is 
termed  the  ventricle  of  the  septum  lucidum,  or  the  fifth  ventricle. 


THE    FIFTH  VENTRICLE. 

This  ventricle  does  not  communicate  with  the  other  ventricular 
cavities.  It  was  originally  a  part  of  the  great  longitudinal  fis- 
sure, but  owing  to  the  union  of  the  hemispheres  by  the  develop- 
ment of  the  corpus  callosum  above  and  the  fornix  below,  that 
space  which  had  been  a  part  of  the  longitudinal  fissure  became 
a  distinct  cavity  with  walls  of  its  own — the  laminai  of  the  septum 
lucidum.     These  lamina;   are  formed  of  the  mesial  wall  of  the 


ANATOMY   OF   INTERIOR   OF   CEREBRAL   HEMISPHERES.  415 

hemispheres,  and  are  thus  composed  of  an  internal  layer  of  gray 
matter,  covered  with  pia  mater,  similar  to  the  cortex  but  much 
more  delicate  in  structure  ;  a  middle  layer  of  white  matter  ;  and 
an  external  layer  of  ependymal  tissue,  covered  by  an  epithelial 
layer  continuous  with  that  lining  the  lateral  ventricle. 


ciiapti:r  XI. 

THE    BLOOD-VESSELS    OF   THE   BRAIN. 

An  accurate  acquaintance  with  the  exact  distribution  of  the 
blood-vessels  that  nourish  the  brain  is  of  great  importance,  be- 
cause of  the  fact  that  very  many  cerebral  affections  are  due  to 
their  rupture  or  to  obstruction  by  emboli  or  thrombi,  all  of  which 
conditions  are  more  frequent  in  the  brain  than  in  any  other 
organ  of  the  body.  This  is  due  to  the  large  size  of  its  main 
trunks  of  supply,  as  well  as  to  their  direct  course  in  the  blood 
stream.  For  this  reason  emboli  are  more  easily  swept  into  the 
vessels  of  the  brain  than  into  those  of  the  other  organs.  Owing- 
to  the  high  arterial  tension  to  which  these  vessels  are  more 
or  less  constantly  subjected,  they  often  early  present  degenerative 
changes  in  their  walls,  which  increases  the  chance  of  rupture  or 
of  the  formation  of  thrombi. 

The  cerebral  blood-vessels  are  arranged  in  two  systems — the 
cortical  and  the  central  or  oranorlionic.  The  former  are  for  the 
nutrition  of  the  convolutions  and  underlving  white  matter,  and 
are  distributed  in  the  pia  mater.  They  consist  of  two  sets, — 
lonof  and  short, — which  enter  the  cortex  at  ricjht  angles  to  its 
surface. 

The  long  arteries,  which  supply  a  considerable  part  of  the 
centrum  semiovale,  pass  through  the  gray  matter,  penetrate  the 
whfte  matter  for  an  inch  or  more,  following  the  course  of  its 
nerve  fasciculi,  and  communicate  with  each  other  by  very  fine 
capillary  branches,  which  form  elongated  plexuses.  Most  of  the 
shorter  ones  are  distributed  to  the  cortex  only,  although  some 
of  the  longer  branches  reach  the  white  matter  just  beneath  the 
cortex.  They  anastomose  very  freely,  forming  distinct  plexuses 
in  the  gray  matter. 

The  central  or  ganglionic  vessels  nourish  the  central  gangh'a 

416 


BLOOD-VESSELS    OF    THE   BRAIN. 


417 


and  adjacent  parts,  and  are  terminal  end  arteries,  there  existing 
no  anastomosis  between  them  and  the  cortical  vessels.  While 
the  terminal  cortical  vessels  anastomose  slightly  with  one  an- 
other, this  is  insufficient,  in  case  of  their  obstruction,  to  pre- 
vent a  local  necrosis  of  the  areas  which  they  nourish.  Hence, 
the  general  statement  may  be  made  that  the  majority  of  the 
arteries  of  the  brain  are  physiologically  end  vessels.* 


Fig.  204. — Distribution  of  Arteries  in  the  Cerebral  Cortex.  —  [After  Dtcrei.) 
I,  I.   Medullary   arteries.      1' ,  \^.   In    groups    between    the    convolutions.      I^^.    Commissural 
arteries.     2,  2.   Arteries  of  the  cortex  cerebri,      a.   Large  meshed  plexus  in  first  layer,     b. 
■  Closer  plexus  in  middle  layer,      c.   Opener  plexus  in  the  gray  matter  next  the  white  sub- 
stance, with  its  vessels  [d). 

The  arterial  supply  to  the  cerebrum  comes  from  two  sources 
— the  internal  carotids  and  the  vertebrals. 


*  Physiologically  considered,  end  arteries  are  such  as  are  found  in  the  brain  or  the 
heart,  obstruction  of  which  causes  local  death  of  the  part  they  nourish.  These  arteries  may 
not  be  strictly  end  arteries  in  the  sense  Cohnheim  intended,  for  many  of  them  anastomose  with 
other  terminal  branches,  but  the  collateral  circulation  thus  established  is  insufficient  of  itself  to 
maintain  the  nutrition  of  the  part  thus  supplied  when  either  terminal  vessel  is  obstructed,  their 
plugging,  either  by  emboli  or  thrombi,  always  resulting  in  local  areas  of  necrosis  or  softening, 
which  usually  give  rise  to  definite  localizing  symptoms. 
27 


4iS  CENTRAL  NERVOUS  SYSTEM. 

CAROTID  ARTERIES. 

The  right  internal  carotid  artery  arises  from  the  innominate 
artery,  while  the  left  has  its  origin  from  the  highest  point  of  the 
arch  of  the  aorta,  both  carotids  dividing  at  the  upper  border  of 
the  thyroid  cartilage  into  external  and  internal  branches,  called 
respectively  the  external  and  internal  carotid  arteries. 

The  internal  carotid  of  each  side,  continuing  upward,  reaches 
the  cavity  of  the  skull  through  the  middle  lacerated  foramen, 
having  passed  through  the  carotid  canal  in  the  petrous  portion 
of  the  temporal  bone.  It  then  passes  through  the  cavernous 
sinus  until  it  reaches  the  anterior  clinoid  process,  where  it  pierces 
the  dura  mater  and  reaches  the  base  of  the  brain  at  the  begin- 
ning of  the  fissure  of  Sylvius.  The  vertebral  arteries,  which 
have  their  origin  from  the  subclavian  arteries,  pass  through  all 
the  foramina  in  the  transverse  processes  of  the  vertebrae  above 
the  fifth  cervical  ;  during  this  course  they  give  off  several  lateral 
spinal  arteries,  whose  medullary  branches  pass  with  the  spinal 
nerves  to  the  spinal  cord,  supplying  it  and  its  membranes.  They 
then  pierce  the  dura  mater  and  reach  the  interior  of  the  skull 
through  the  foramen  mas^num.  It  is  interestino-  to  note  that, 
owing  to  the  direct  course  of  the  blood-stream  in  the  left  carotid 
artery, — it  being  continuous  with  that  in  the  aorta, — emboli,  which 
are  frequently  dislodged  from  diseased  cardiac  valves,  more 
frequently  pass  into  this  vessel  than  into  the  right,  because  the 
latter  artery  arises  from  the  innominate,  which  is  given  off  from 
the  aortic  arch  at  an  angle  with  the  course  of  the  blood-stream. 
This  fact  remains  true  for  the  vertebrals :  the  right  has  its  origin 
from  the  subclavian  after  the  latter  vessel  becomes  horizontal, 
while  the  left  arises  from  the  subclavian  in  its  upward  course, 
and  hence  is  in  direct  line  of  the  blood-stream. 

The  internal  carotid  artery,  after  reaching  the  base  of  the 
brain,  rests  on  the  anterior  perforated  space  at  the  inner  portion 
of  the  Sylvian  fissure,  between  the  optic  and  oculomotor  nerves. 
It  terminates  in  the  followino-  branches:  the  anterior  and  middle 
cerebral,  the  posterior  communicating,  and  the  anterior  choroid 
arteries. 


Fig.  205. — The  Arteries  of  the  Base  of  the  Cerebrum. — [G.D.  T.,  after  Buret,  ana 

fro??i  nature,  from  Quain.') 

On  the  left  side  of  the  brain  the  temporal  lobe  is  cut  away  so  as  to  open  the  inferior  and  poste- 
rior horns  of  the  lateral  ventricle.  The  mid-brain  is  divided  close  above  the  pons  and  the 
posterior  cerebral  arteries  are  cut  at  their  origin  from  the  basilar. 

Central  arteries  (to  the  basal  ganglia)  :  am.  Anteromesial  group  arising  from  the  anterior  cere- 
bral, al.  Anterolateral  group,  from  the  middle  cerebral.  pm,pl  (on  the  optic  thalamus). 
Posteromesial  and  posterolateral  groups,  from  the  posterior  cerebral. 

Choroid  arteries  :  a  ch.  Anterior,  from  the  internal  carotid.  /  ch  (on  the  splenium).  Posterior, 
from  the  posterior  cerebral. 

Periphe7-al  arteries  :  1,1.  Inferior  internal  frontal,  from  the  anterior  cerebral.  2.  Inferior  ex- 
ternal frontal.  3.  Ascending  frontal.  4.  Ascending  parietal,  and  5,  temporoparietal, 
from  the  middle  cerebral.  6.  Anterior  temporal,  7,  posterior  temporal,  and  8,  occipital, 
from  the  posterior  cerebral. 

419 


BLOOD-VESSELS    OF    THE    BRAIN.  421 

THE  ante;jiior  cerebral  artery. 

The  anterior  cerebral  artery  passes  forward  and  inward  across 
the  anterior  perforated  space  to  reach  the  inferior  longitudinal 
fissure  between  the  frontal  lobes,  where  it  lies  close  to  its  fellow 
of  the  opposite  side,  and  gives  jDff  a  branch  of  communication 
with  that  vessel  called  the  anterior  communicating  artery.  It 
then  passes  forward  around  the  genu  of  the  corpus  callosum, 
reaching  its  superior  portion,  and  after  giving  off  its  cortical 
branches,  it  courses  backward  to  terminate  with  the  posterior 
cerebral  artery. 

The  branches  of  the  anterior  cerebral  artery  are  the  anterior 
communicating,  the  central  or  ganglionic,  the  commissural,  and 
the  cortical.  The  anterior  communicating  artery  is  a  small, 
transverse  branch,  about  two  lines  in  length,  which  connects  the 
two  anterior  cerebral  arteries.  This  communicating  branch 
gives  off  two  or  three  of  the  anteromedian  arteries,  which  pass 
to  the  head  of  the  caudate  nucleus.  The  central  or  gang- 
lionic branches  are  the  anteromedian  group  of  vessels,  most  of 
which  come  from  the  anterior  cerebral,  while  a  few  come  from 
the  anterior  communicating.  They  pass  through  the  anterior 
perforated  space  and  lamina  cinerea  to  be  distributed  to  the 
head  of  the  caudate  nucleus. 

The  commissural  branches  supply  the  corpus  callosum.  The 
cortical  branches  are  the  orbital,  the  marginofrontal,  the  calloso- 
marginal,  and  the  quadrate.  The  orbital  branches  supply  the 
inner  part  of  the  orbital  lobe  and  the  olfactory  bulb.  The 
marginofrontal  artery,  which  comes  from  the  anterior  cerebral 
as  it  rests  on  the  corpus  callosum,  supplies  the  marginal  gyrus, 
the  convex  surface  of  the  superior  and  middle  frontal  gyri,  and 
the  superior  portion  of  the  ascending  frontal  convolution.  The 
callosomarginal  branch  is  distributed  to  the  gyrus  fornicatus. 
The  quadrate  artery  nourishes  the  quadrate  lobe,  or  precuneus. 
It  will  thus  be  seen  that  the  cordcal  branches  of  the  anterior 
cerebral  artery  supply  the  entire  median  portion  of  the  cere- 
bral hemisphere  as  far  back  as  the  cuneus,  the  first  and  second 
frontal,  the  upper  part  of  the  ascending  frontal,  together  with 
the  orbital  lobe  and  olfactory  bulb. 


422 


CENTRAL  NERVOUS  SYSTEM. 


THE   MIDDLE  CEREBRAL  OR  SVLVL\N  ARTERY. 

The  middle  cerebral  or  Sylvian  artery,  the  largest  terminal 
branch  of  the  internal  carotid,  lies  in  the  Sylvian  fissure.  Its  course 
is  forward  and  outward  until  it  reaches  the  island  of  Reil,  where 
it  divides  into  five  cortical  branches,  which  lie  in  the  sulci  of  the 
insula  ;  these  branches  are  then  continued  on  to  the  convex  sur- 
face of  the  hemisphere,  to  supply  a  part  of  the  frontal,  most  of 
the  central,  and  the  parietal  convolutions,  as  well  as  a  large  part 
of  the  temporal  lobe.   The  cortical  branches  of  the  Sylvian  are  the 


Fig.  206. — Cortical  Distributidn  ■  >!    nii.  Middle  Cerebral  Artery  (Diagrammatic). 

— [G.   D.  T.  after  Charcot,  from  Quahi.) 
CENT.   Anterolateral  group  of  central  arteries.      I.   Inferior  external  frontal  artery.     2.   Ascend- 
ing frontal  artery.      3.   Ascending  parietal  arterj-.     4.    Parietotemporal  artery. 


inferior  frontal,  the  ascending  frontal,  the  ascending  parietal,  the 
parietotemporal,  and  the  sphenoid. 

The  first  or  inferior  frontal  artery  is  distributed  to  the  convex 
surface  of  the  inferior  frontal  convolution.  The  second  or 
ascending  frontal  supplies  the  lower  two-thirds  of  the  ascending 
frontal  and  the  root  of  the  second  frontal,  the  upper  third  of  the 
ascending  frontal  being  supplied  by  the  marginofrontal  branch 
of  the  anterior  cerebral  artery.  The  third  or  ascending  parietal 
artery  is  distributed  to  the  whole  of  the  ascending  parietal,  the 
superior   parietal,  and  that  part  of  the  inferior  parietal  lobule 


BLOOD-VESSELS    OF    THE   BRAIN. 


423 


adjacent  to  the  ascending  parietal  gyrus.  The  fourth,  the 
parietotemporal  artery,  supplies  the  supramarginal,  the  angular, 
the  posterior  part  of  the  inferior  parietal,  and  the  first  and  second 
temporal  gyri.  The  fifth  or  sphenoid  artery  supplies  the  an- 
terior part  of  the  first  and  most  of  the  second  temporal  convo- 
lutions. 

The  Central  or  Ganglionic  Branches  of  the  Middle 
Cerebral. — These  branches  arise  from  the  middle  cerebral 
close  to  its  origin.  They  consist,  first,  of  two  small  vessels 
which  pass  through  the  inner  part  of  the  floor  of  the  Sylvian 
fissure  to  the  head  of  the  caudate  nucleus  ;  and,  second,  of 
numerous  small  vessels — the  anterolateral  arteries — which  come 


Fig.  207. — Diagram  of  the  Blood-supply  to  the  Central  Ganglia  by  the  Lentic- 

ULOSTRIATE   ARTERIES,    EXTERNAL    {E)    AND    INTERNAL    (/). — {After  Duret.) 

HIV.  Third  ventricle.      PP.    Pillars  of  the  fornix.      Mid.  C.   Middle  cerebral  artery. 


off  from  the  Sylvianat  right  angles  and  pass  through  the  anterior 
perforated  space  to  be  distributed  to  the  caudate  nucleus,  except 
its  head,  to  the  lenticular  nucleus,  the  internal  capsule,  the  ex- 
ternal capsule,  and  a  part  of  the  optic  thalamus. 

These  central  or  ganglionic  branches  of  the  Sylvian  artery 
are  grouped  by  Duret  into  internal  and  external  branches. 
The  internal  branches  pass  through  the  inner  segments  of  the 
lenticular  nucleus  and  are  distributed  to  that  nucleus  and  to  the 
internal  capsule.  The  external  vessels,  which  are  divisible  into  an 
anterior  and  a  posterior  set,  pass  upward  outside  of  the  lenticu- 
lar nucleus,  pierce  the  third  segment  of  the  lenticular  nucleus,  and 
pass  to  the  internal  capsule.    The  anterior  branches  are  called  the 


424  CENTRAL  NERVOUS  SYSTEM. 

lenticulostriate  arteries  ;  they  pass  to  the  lenticular  and  caudate 
nuclei,  except  the  head  of  the  latter.  The  posterior  branches, 
or  the  lenticulo-optic  arteries,  supply  the  posterior  parts  of  the 
internal  capsule  and  the  anterior  and  inner  parts  of  the  optic 
thalamus.  The  largest  of  the  lenticulostriate  arteries,  which 
passes  between  the  lenticular  nucleus  and  the  external  capsule, 
and  terminates  in  the  caudate  nucleus,  is  called,  from  its  ten- 
dency to  rupture,  "  the  artery  of  cerebral  hemorrhage " 
(Charcot). 


POSTERIOR  COMMUNICATING  ARTERY. 

The  posterior  communicating  artery  arises  from  the  back 
part  of  the  internal  carotid  before  that  vessel  divides  into  the 
anterior  and  middle  cerebral  arteries.  Occasionally  it  arises 
from  this  latter  vessel.  The  communicating  artery  passes  back- 
ward over  the  optic  tract  and  crus  cerebri,  and  joins  the  poste- 
rior cerebral,  a  branch  of  the  basilar.  In  its  course  it  gives  oft 
small  branches  of  supply  to  the  dorsal  portion  of  the  optic 
chiasm,  to  crus  cerebri,  infundibulum,  and  pituitary  body,  and  to 
the  corpora  mammillaria.  From  the  posterior  part  of  this  com- 
municatino-  branch  a  few  small  vessels  are  criven  off,  which,  with 
similar  vessels  from  the  posterior  cerebral,  form  the  postero- 
median oranoflionic  branches. 


THE  ANTERIOR  CHOROID  ARTERY. 

The  anterior  choroid  artery  is  a  small,  slender  branch  from 
the  back  part  of  the  internal  carotid,  just  external  to  the  poste- 
rior communicating  ;  it  courses  backward  on  to  the  optic  tract 
and  crus  cerebri,  then  passes  beneath  the  uncinate  gyrus, 
enters  the  transverse  fissure  at  the  lower  part  of  the  descend- 
ing horn  of  the  lateral  ventricle,  and  supplies  the  hippocampus 
major,  or  cornu  ammonis,  the  corpus  fimbriatum,  and  the  cho- 
roid plexus. 


BLOOD-VESSELS    OF    THE   BRAIN.  425 

THE  VERTEBRAL  ARTERIES. 

The  vertebral  arteries,  after  reaching  the  cranial  cavity 
through  the  foramen  magnum,  course  along  the  ventral  portion 
of  the  medulla  oblongata  until  they  approach  the  lower  border 
of  the  pons  Varolii,  where  they  unite  to  form  the  basilar  artery, 
which  is  a  mere  prolongation  of  them.  In  their  intracranial 
course  each  vessel  gives  off  the  following  branches  :  the  poste- 
rior meningeal,  the  anterior  and  posterior  spinal,  and  the 
posterior  inferior  cerebellar  artery.  The  posterior  meningeal  is 
a  srhall  vessel  which  leaves  the  vertebral  at  the  foramen  mag- 
num ;  it  supplies  the  falx  cerebelli  and  the  bone  and  dura  mater 
of  the  posterior  fossa  of  the  skull.  The  anterior  and  posterior 
spinal  arteries  are  described  in  connection  with  the  blood-supply 
of  the  spinal  cord.  The  posterior  inferior  cerebellar  arteries 
are  to  be  considered  with  the  description  of  the  nutrient  vessels 
of  the  cerebellum,  pons,  and  medulla. 

THE    BASILAR   ARTERY. 

The  basilar  artery,  a  short  but  large  vessel,  is  formed  by  the 
union  of  the  two  vertebrals.  It  rests  in  the  median  groove  on 
the  ventral  surface  of  the  pons,  and  extends  from  its  inferior  to 
its  upper  border,  where  it  terminates  by  dividing  into  two 
branches — the  posterior  cerebral  arteries.  The  branches  of  the 
basilar  are  the  transverse  or  pontal,  the  internal  auditory,  the 
anterior  cerebellar,  the  superior  cerebellar,  and  the  posterior 
cerebral.  The  pontal  as  well  as  the  cerebellar  branches  will  be 
described  in  connection  with  the  blood-supply  to  the  cerebellum, 
pons,  and  medulla.  The  internal  auditory  artery  passes  with 
the  auditory  nerve  into  the  internal  auditory  meatus  and  is  dis- 
tributed to  the  internal  ear  (Fig.  209). 


THE  POSTERIOR  CEREBRAL  ARTERIES. 

The  posterior  cerebral  arteries,  the  terminal  branches  of  the 
basilar,  wind  around  the  crura  cerebri,  and  after  receiving  the 
posterior  communicating  branches  from  the  internal  carotids. 


426  CENTRAL  NERVOUS  SYSTEM. 

pass  backward  to  reach  the  under  surface  of  the  cerebral  hemi- 
spheres, and  terminate  in  three  branches,  which  are  distributed 
to  the  occipital  and  temporal  lobes.  The  branches  of  the  pos- 
terior cerebral  are  the  central,  or  ganglionic,  and  the  cortical,  or 
terminal.  The  central,  or  ganglionic,  consist  of  the  postero- 
median, the  posterior  choroid,  and  the  posterolateral.  The 
posteromedian  arteries  consist  of  several  small  vessels  which 
arise  from  the  posterior  cerebral  close  to  its  origin.  These 
vessels,  in  connection  with  a  few  bearing  the  same  name  from 
the  posterior  communicating,  pass  through  the  posterior  perfor- 
ated space  to  supply  the  inner  part  of  the  optic  thalamus  and 


walls  of  the  third  ventricle.  The  posterior  choroid  branch, 
which  supplies  the  velum  interpositum  and  choroid  plexus, 
passes  through  the  transverse  fissure.  The  posterolateral 
vessels  take  their  origin  from  the  posterior  cerebral  after  it  has 
passed  around  the  crus  cerebri ;  they  give  branches  to  the  crus 
cerebri,  corpora  quadrigemina,  and  posterior  part  of  the  optic 
thalamus.  The  cortical  or  terminal  branches,  three  in  number, 
are  distributed  as  follows:  (i)  A  branch  to  the  uncinate  con- 
volution ;  (2)  a  branch  to  the  superior  part  of  the  temporal 
lobe  ;  (3)  the  temporo-occipital  branch  to  the  cuneus,  the 
lingual  gyrus,  and  the  outer  surface  of  the  occipital  lobe. 


Fig.  208. — Diagram  Showing  the  Areas  of  Cortical  Distribution  of  the  Anterior, 
Middle,  and  Posterior  Cerebral  Arteries  Respectively. — [E.  A.  S.,from  Qiiain.) 

A.  Lateral  aspect  (see  opposite  page).  B.  Mesial  aspect.  C.  Basal  aspect.  The  area  supplied 
by  the  middle  cerebral  frequently  extends  to  the  upper  border  of  the  hemisphere  in  the 
region  of  the  parietal  lobe,  and  therefore  somewhat  further  than  is  represented  in  A. 

427 


BLOOD-VESSELS    OF    THE    BRAIN. 


429 


THE   CIRCLE  OF  WILLIS. 

The  branches  of  the  internal  carotids  and  vertebrals  form  at 
the  base  of  the  brain  a  remarkable  anastomosis,  called  the  circle 
of  Willis.  This  circle  is  completed  anteriorly  by  the  anterior 
cerebral  arteries  and  their  branch  of  communication,  the  anterior 


a..e.e,rob.post . 


;a  cci  eh.  aixp^ 


Ci.ce.rch. 

77ZOLf, 


a .  ot-Teh.  u 


Fig.  209. — Arteries  of  the  Anterior  Surface   of   the  Pons  and  Medulla.  —  {Afiei 

Buret. ) 

a.  cereb.  post.  Posterior  cerebral  artery.  a.  cereb.  sup.  Superior  cerebellar  artery,  a.  cereb. 
tnoyen.   Middle  cerebellar  artery,     a.  cereb.  iitf.   Inferior  cerebellar  artery. 

/.  Root-arteries  of  spinal  accessory  nerve.  2.  Anterior  spinal  artery,  j.  Root-arteries  of  pneu- 
mogastric  nerve.  4.  Root-arteries  of  glossopharyngeal  nerve,  j".  Root-arteries  of  the  oculo- 
motor nerve.  6.  Root-arteries  of  the  facial  and  acoustic  nerves.  7.  Root-arteries  of  the 
trigeminus  nerve.     8.   Root  arteries  of  hypoglossal  nerve. 


communicating  ;  posteriorly,  by  the  posterior  cerebrals  and  point 
of  the  basilar  ;  and  laterally,  by  the  internal  carotids  and  pos- 
terior communicating^  arteries.  This  circle  of  anastomosis 
serves  to  equalize  the  blood-flow  to  the  brain,  and  is  the  only 
means   of  communication  between   the  cortical   and  central  or 


430 


CENTRAL  NERVOUS  SYSTEM. 


ganglionic  blood-vessels.  If  either  of  the  main  trunks  (carotids 
or  vertebrals)  are  obstructed,  the  nutrition  of  the  parts  of  the 
brain  supplied  by  the  branches  of  the  obstructed  vessels  is  not 
interfered  with,  because  they  are  supplied  through  the  circle  of 
Willis  by  the  remaining  vessels,  which  are  pervious. 

The  cerebellum,  the  pons  Varolii,  and  the  medulla  oblongata 
are  supplied  with  branches  from  the  vertebrals  and  basilar 
arteries. 


eh.  uT.f 

CO.  ypnx  post . 


Fig.  2IO. — Arteries  of  the  Posterior  Surface  of  the  Medulla. — [After  Dtiret.) 
(1.  cereb.  inf.    Inferior  cerebellar  artery,      a.  spin.  post.  Posterior  spinal  artery. 


BLOOD-VESSELS  OF  THE    CEREBELLUM. 

The  blood-supply  to  the  cerebellum  is  derived  from  three  ves- 
sels— the  superior,  the  middle,  and  the  inferior  cerebellar  arteries. 
The  superior  cerebellar  arteries  take  their  origin  from  the  basilar 
close  to  its  point  of  division  into  the  posterior  cerebral  arteries. 
Each  vessel  courses  backward  and  outward  over  the  pons 
Varolii,   being  separated    from    the    posterior    cerebral    arter)\ 


BLOOD-VESSELS    OF    THE   BRAIN.  431 

whose  course  it  resembles,  by  the  motor  oculi,  or  third  cranial 
nerve.  It  then  courses  around  the  crus  cerebri,  parallel  with 
the  fourth  cranial  nerve,  and  reaches  the  upper  surface  of  the 
cerebellum,  where  it  divides  into  an  internal  or  superior  vermi- 
form branch,  and  an  external  or  hemispheral  branch.  The 
former  vessel  passes  backward  along  the  superior  vermiform 
process,  anastomoses  with  the  artery  of  the  opposite  side,  and 
when  it  reaches  the  posterior  notch  of  the  cerebellum  it  joins 
the  inferior  vermiform  artery,  a  branch  of  the  posterior  inferior 
cerebellar  artery.  The  external  or  hemispheral  branch  runs 
backward  over  the  superior  surface  of  the  cerebellum,  supplying 
it,  and  terminates  near  the  posterior  part  of  this  surface,  where 
it  anastomoses  with  the  terminal  hemispheral  branch  of  the  pos- 
terior inferior  cerebellar  artery.  This  artery  also  supplies 
branches  to  the  velum  interpositum,  the  superior  medullary 
velum,  or  valve  of  Vieussens,  the  corpora  quadrigemina,  and  the 
pineal  gland. 

The  middle  cerebellar — also  called  the  anterior  inferior  cere- 
bellar— arteries  are  branches  of  the  basilar,  and  originate  from 
that  vessel  just  above  the  inferior  border  of  the  pons  ;  their 
course  is  downward  and  outward  across  the  pons  to  the  anterior 
portion  of  the  under  surface  of  the  cerebellum,  which  they  sup- 
ply. They  anastomose  with  the  posterior  inferior  cerebellar 
artery.  This  vessel,  at  the  beginning  of  its  course,  is  crossed 
by  the  abducens  or  sixth  cranial  nerve,  and  just  as  it  passes 
upon  the  inferior  surface  of  the  cerebellum,  it  lies  close  to  the 
facial  and  auditory  nerves.  In  its  course  across  the  pons  it 
gives  off  several  rather  large  vessels  for  the  supply  of  the  middle 
cerebellar  peduncles. 

The  inferior  cerebellar  arteries  are  also  known  as  the  pos- 
terior inferior  cerebellar.  This  latter  name  serves  to  distinguish 
them  from  the  middle  cerebellar,  which  have,  unfortunately,  been 
named  the  anterior  inferior  cerebellar  arteries.  These  two  ves- 
sels are  the  largest  branches  of  the  vertebrals,  and  have  their 
origin  from  them  opposite  the  lateral  surfaces  of  the  medulla 
near  Its  middle  portion.  Each  vessel  passes  outward  and  back- 
ward across  the  restiform  body  and  between  the  pneumogastric 
and  hypoglossal  nerve-roots  ;  it  then  goes  to  the  under  surface 


432  CENTRAL  NERVOUS  SYSTEM. 

of  the  cerebellum,  where  it  divides  Into  two  branches — an  in- 
ternal, or  inferior  vermiform,  and  an  external,  or  hemispheral. 
The  inferior  vermiform  branch  passes  backward  between  the 
vermiform  process  and  the  cerebellar  hemisphere,  supplies  the 
vermiform  process,  and  anastomoses  with  the  vessels  of  the  oppo- 
site side  and  the  superior  vermiform,  a  branch  of  the  superior 
cerebellar  artery.  The  external  or  hemispheral  branch  is  dis- 
tributed to  the  under  surface  of  the  cerebellum,  and  anastomoses 
along  its  outer  margin  with  the  middle  and  superior  cerebellar 
arteries.  This  vessel  also  gives  branches  of  supply  to  the  choroid 
plexus  of  the  fourth  ventricle  and  to  the  restiform  bodies. 


ARTERIAL  SUPPLY  TO  THE  PONS  VAROLII  AND 
MEDULLA  OBLONGATA. 

The  pons  \'arolii  and  medulla  oblongata  receive  their  arterial 
supply  from  a  series  of  small  vessels  which  come  off  directly 
from  the  basilar  and  vertebral  arteries  and  from  their  branches 
— the  anterior  and  posterior  spinal  and  the  inferior  cerebellar 
arteries.  The  branches  of  the  above-mentioned  arteries  which 
reach  the  interior  of  the  pons  and  medulla  have  been  divided 
by  Duret  into  the  three  following  sets : 

First  Set,  the  Median  Arteries. — These  are  small  vessels  which 
pass  parallel  to  one  another  through  the  median  plane  of  the 
pons  and  medulla  to  reach  the  floor  of  the  fourth  ventricle,  where 
they  terminate  by  dividing  into  fine  capillary  plexuses  for  the 
supply  of  the  cranial  nerve  nuclei  and  the  beginning  of  their 
nerve-roots. 

The  second  set,  or  root  arteries,  pass  in  a  transverse  manner 
around  the  outer  portion  of  the  pons  and  medulla  to  reach  the 
point  of  emergence  of  the  roots  of  the  cranial  nerves,  where  they 
divide  into  two  branches — central  and  peripheral.  The  central 
branch  continues  with  the  nerve  to  its  nucleus  of  origin,  sub- 
dividing into  a  few  parallel  branches  which  terminate  into  a 
capillary  plexus  about  the  nucleus,  inosculating  with  small  twigs 
from  the  median  arteries.  The  peripheral  branch  is  distributed 
alonor  the  nerve-roots. 

The  third  or  lateral  set  of  vessels   continue  around  the  lateral 


BLOOD-VESSELS    OF    THE   BRAIN. 


433 


and  anterior  columns  of  the  medulla  to  be  distributed  to  the 

restiform  and  olivary  bodies  as  well  as  to  the  anterior  pyramids. 

The  median  arteries  to  the  pons  consist  of  a  large  number  of 

parallel  coursing  vessels,  which  come  off  directly  from  the  basilar 

ce-rch-joost. 


■ci.cereb. 


■a .  vert,  droilc. 
-a.SPt^ri  pc^t. 


Fig.  211. — Anterior  and  Posterior  Median  Arteries  of  the  Pons  and  Medulla. — 

{After  Diiret.) 
a.cereb.post.     Posterior   cerebral    artery.       a.cereb.siip.     Superior    cerebellar    artery.       a.cereb. 

nioyejzne.  Middle  cerebellar  artery,     ti'ofic  basilaire.   Basilar  artery,     a.vert.droite,  and  ar. 

vert. gauche.    Right    and    left    vertebrals.     a.sp.ant.    Anterior   spinal    artery,     a.spin.post. 

Posterior  spinal  artery. 


and,  passing  backward,  reach  the  floor  of  the  fourth  ventricle, 
where  they  terminate  by  subdividing  into  capillary  plexuses  for 
the  nutrition  of  the  following  cranial  nerve  nuclei :  the  oculo- 
motor, trigeminal,  abducens,  facial,  auditory,  glossopharyngeal, 
28 


434 


CENTRAL  NERVOUS  SYSTEM. 


and  pneiimog-astric.  These  branches  also  nourish  the  motor 
nerve-roots  as  they  issue  from  their  nuclei  of  origin,  and  the 
sensory  nerve-roots  as  they  pass  into  their  respective  nuclei. 
These  median  vessels  anastomose  with  the  termination  of  the 
nerve  arteries. 

The  root-arteries  to  the  pons  are  distributed  to  the  nerve- 
roots  of  the  oculomotor,  trigeminal,  abducens,  and  facial  nerves. 

The  median  arteries  to  the  medulla  come  from  the  vertebrals 
and  anterior  spinal  arteries,  after  pursuing  a  course  similar  to 


^fiin.j'ost 


«"^        "*"^-<.t  vt.rlelfT'. 

Fig.  212. — Diagram  to  Show  Plan  of  Uistkibution  of  the  Arteries  of  the 

Medulla. — {After  Buret.) 

a.spin.post.   Posterior  spinal  artery,      a.vertebr.   Vertebral   artery,     a. spin. ant.    Anterior  spinal 

artery. 


the  median  vessels  of  the  pons,  and  are  distributed  to  the  lower 
part  of  the  facial,  the  pneumog'astric,  hypoglossal,  and  spinal 
accessory  nuclei,  and  to  their  nerve-roots. 

The  root-arteries  to  the  medulla  give  off  collaterals  which, 
with  branches  from  the  anterior  spinal  arteries,  are  distributed 
to  the  anterior  pyramids,  the  hypoglossal  nerve-roots,  and  the 
olivary  bodies.  The  inferior  cerebellar  arteries  give  off  several 
lateral  branches  which  go  to,  and  nourish,  the  restiform  bodies 
and  the  formatio  reticularis.  These  vessels  also  give  off  poste- 
rior branches  for  distribution   to  the  choroid  plexus  and  fourth 


BLOOD-VESSELS    OF    THE    BRAIN.  435 

ventricle.  The  posterior  aspect  of  the  medulla  receives  branches 
of  supply  from  the  posterior  spinal  arteries,  which  nourish 
chiefly  the  posterior  columns  or  pyramids. 


THE  VENOUS    SYSTEMS    OF    THE    BRAIN. 

CHARACTERISTICS    OF   THE  VEINS   AND    THE   VENOUS 
CIRCULATION. 

The  veins  of  the  brain  differ  from  those  in  the  other  parts  of 
the  body  in  the  following  particulars:  (i)  Their  walls  are  ex- 
ceedingly thin,  owing  to  the  absence  of  a  muscular  coat ;  (2) 
they  possess   no  valves  ;    (3)    they  empty  into   venous   sinuses; 

(4)  they  frequently  anastomose  by  small  and  large  branches  ; 

(5)  they  are  less  in  number  but  much  more  capacious  than  the 
corresponding  arteries  ;  (6)  the  circulation  through  the  superior 
veins  of  the  cerebrum  which  empty  into  the  superior  longitud- 
inal sinus  is  greatly  retarded,  first,  by  the  fact  that  they  are 
ascending  in  their  course,  and  hence  are  not  assisted  by  gravity  ; 
and,  secondly,  because  they  empty  into  the  superior  longitudinal 
sinus  in  a  direction  opposite  to  the  current  of  blood  in  that 
sinus. 

The  circulation  is  further  impeded  by  the  absence  of  valves 
and  muscular  tissue,  and  by  the  presence  in  the  sinuses  of 
fibrous  bands  which  stretch  across  their  lumen.  Dwight  has 
suggested  that,  owing  to  the  proximity  of  the  carotid  artery  to 
the  jugular  vein,  the  circulation  in  that  vein  is  hindered  by  the 
pulsations  of  the  artery,  thus  tending  to  cause  a  retardation  of 
the  venous  circulation  of  the  brain.  These  facts  help  us  to 
understand  why  venous  thrombi  so  often  occur  in  the  veins  and 
sinuses  in  many  of  the  acute  infectious  diseases,  and  Gowers 
aptly  states  that  the  marvel  is  that  thrombosis  is  not  more 
common  than  it  is. 


THE    CEREBRAL    VEINS. 

The  cerebral  veins  may  be  divided  into  two  sets — superficial 
or  hemispheral,  and  deep  or  ganglionic.  The  superficial  or 
hemispheral   veins   are  further  subdivided  into  the  veins  of  the 


436 


CENTRAL  NERVOUS  SYSTEM. 


base,  which  are  found  along-  the  middle  portion  of  the  base  of 
the  brain,  and  into  the  veins  of  the  convolutions,  which  course 
in  the  meshes  of  the  pia  mater  covering  the  median  and  convex 
surface  of  the  hemisphere.     The  deep  or  ganglionic  set  of  veins 


Fic.  213. — Superficial  Veins  ok  the  Base  of  the  Brain. — {After  Testut.) 
I.   Lateral  sinus.     2.   Superior  longitudinal  sinus.     3.   Trunk  resulting  from  the  union  of  the 
veins  of  Galen  with  the  basilar  veins.     4.   Anterior  communicating  vein.     5.   Middle  cere- 
bral vein.     6.  Basilar  vein.     7.   Posterior  communicating.     8.    Anterior  cerebral  vein.     9. 
Vein  of  the  cornu  ammonis.      10.   Great  anastomotic  vein  of  Trolard. 


originates  in   the  central  ganglia,  and  unites  to  form  two  rather 
large  trunks — the  veins  of  Galen. 

The  Superficial  Veins. — The  superficial  veins  of  the  base 
are  the  anterior  cerebral,  the  middle  cerebral,  and  the  basilar. 


BLOOD-VESSELS    OF    THE   BRAIN.  437 

The  anterior  cerebral  vein,  smaller  than  the  corresponding 
artery,  drains  the  median  surface  of  the  frontal  lobe  and  the 
convex  surface  of  the  corpus  callosum,  and,  coursing  downward 
and  backward,  unites  with  the  middle  cerebral  to  form  the 
basilar. 

The  middle  cerebral  vein,  smaller  than  the  corresponding 
artery,  is  situated  in  the  fissure  of  Sylvius  and  overlying  the  con- 
volutions of  the  island  of  Reil,  receiving  its  blood  from  these 
convolutions. 

The  basilar  is  a  large  vein  formed  by  the  junction  of  the  ante- 


FiG.  214. — Superficial  Veins  of  the  Internal  Surface  of  the  Left  Hemisphere. — 

{After   Testnt.) 

I.    Superior  longitudinal  sinus.      2.   External  ascending  cerebral  veins.      3.   Venous  trunk  due 

to  union  of  veins  of  Galen.     4.   Basilar  vein. 

rior  and  middle  cerebral  veins  ;  its  course  is  backward  across 
the  cerebral  peduncle  and  around  the  corpora  quadrigemina, 
uniting  at  the  middle  line  with  its  fellow  of  the  opposite  side 
and  with  the  veins  of  Galen  to  form  the  straight  sinus.  It 
drains  the  optic  tract  and  chiasm,  infundibulum,  corpora  mam- 
millaria,  ventral  surface  of  the  cerebral  peduncles,  and  a  part 
of  the  basal  surface  of  the  temporosphenoid  lobe.  The  two 
basilar  veins  are  united  in  front  of  the  pons  VaroHi  by  the  pos- 
terior communicating  vein,  and  the  anterior  cerebral  veins  are 


43^ 


CENTRAL  NERVOUS  SYSTEM. 


united  in  front  by  the  anterior  communicating  vein,  thus  forminor 
a  venous  anastomotic  circle,  similar  to  the  circle  of  Willis. 

The  P'^cins  of  the  ConvoliUions. — The  veins  of  the  convolutions 
may  be  grouped  into  three  systems.  The  first  system  consists 
of  numerous  smaller  systems  which  collect  blood  from  the 
median  surface  of  the  cerebral  hemisphere.  Most  of  these 
ascend  to  empty  into  the  superior  longitudinal  sinus.  Some 
descend  to  empty  into  the  inferior  longitudinal  sinus,  while  a  few 


Fig.  215. — Superficial  Veins  of  the  External  Surface  of  the  Left  Hemisphere. 

{After   Testut.) 
I.   Great  anastomotic  vein  of  Trolard.     2.   Lateral  sinus. 


descend  to  empty  either  into  the  anterior  cerebral  vein  or  the 
vein  of  Galen. 

The  second  system  consists  of  numerous  vessels  which  drain 
the  external  surface,  the  cortex,  and  the  underlying  white  matter 
of  the  cerebrum,  the  long  venules  extending  upward  from  the 
capillary  plexuses  of  the  centrum  ovale,  the  short  venules  col- 
lecting the  blood  from  the  capillary  plexuses  of  the  gray  matter. 
They  are  divisible  into  two  sets,  a  superior  and  an  inferior.  The 
superior  set  ascends  to  empty  into  the  superior  longitudinal 
sinus,  and  consists  of  several  (eight  to  twelve)  veins  which  anas- 


BLOOD-VESSELS    OF    THE    BRAIN. 


439 


tomose  freely  with  one  another  and  collect  the  blood  from  the 
superior  convolutions  of  the  frontal,  parietal,  and  occipital 
lobes. 

The  inferior  set  descend  to  empty  into  the  inferior  longitudinal, 
lateral,  superior  petrosal,  or  cavernous  sinuses,  collecting  blood 
from  the  inferior  part  of  the  frontal,  parietal,  and  occipital  lobes. 
A  large  vein  of  considerable  importance,  the  great  anastomotic 
vein  of  Trolard,  extends  from  the  superior  longitudinal  sinus 
above  to  the  cavernous  or  the  superior  petrosal  sinuses  below. 
This  vein  has  a  course  parallel  to  the  fissure  of  Rolando  and,  at 


Fig.  2i6. — Veins  of  Galen  or  the  Deep  Cerebral  Veins. — [After  Van  GeJmchten.) 

the  level  of  the  fissure  of  Sylvius,  passes  forward  through  that 
fissure  to  the  sinus  before  mentioned.  On  its  downward  course 
it  receives  many  anastomotic  as  well  as  terminal  branches  from 
the  neigrhborinor  convolutions,  and  as  it  turns  down  alono-  the  fis- 
sure  of  Sylvius,  it  receives  a  large  branch  which  brings  this  vein 
into  anastomotic  relations  with  the  lateral  sinus,  called  the  pos- 
terior anastomotic  vein  of  Labbe. 

The  third  system  consists  of  numerous  small  vessels  which 
drain  the  basal  surface  of  the  cerebrum,  and  emptying  in  front 
into  the  anterior  cerebral  vein  or  the  beginning  of  the  superior 


440  CENTRAL   NERVOUS   SYSTEM. 

longitudinal    sinus,   and   in    the   middle  and    posterior    regions 
emptying  into  the  middle  cerebral  vein  or  lateral  sinus. 

The  Deep  Cerebral  Veins. — The  deep  or  ganglionic  veins 
receive  their  blood  Irom  the  central  ganglia,  from  the  ventricular 
walls  and  underlying  white  matter,  and  from  the  choroid  plexuses. 
They  form  two  large  venous  trunks, — the  veins  of  Galen, — which 
extend  between  the  layers  of  the  choroid  plexuses  to  empty 
into  the  basilar  veins  close  to  their  exit  into  the  straight  sinus. 
The  veins  of  Galen  are  formed  by  the  veins  of  the  corpora 
striata,  the   choroid  veins,  and  the  veins  of  the  septum  lucidum. 

The  vein  of  each  corpus  striatum  is  quite  large,  and  is  located 
in  a  groove,  the  semicircular  sulcus,  which  separates  the  optic 
thalamus  from  the  caudate  nucleus.  It  receives  many  small 
veins  from  the  optic  thalamus,  caudate  and  lenticular  nuclei, 
and  the  internal  capsule,  and  at  the  foramen  of  Monro  joins  the 
choroid  vein  to  form  the  vein  of  Galen. 

Each  choroid  vein  courses  along  the  outer  border  of  the 
choroid  plexus  from  the  descending  cornu  of  the  lateral  ven- 
tricle, and  extends  upward  and  forward  to  the  foramen  of 
Monro,  where  it  joins  the  vein  of  the  corpus  striatum  to  form 
the  vein  of  Galen  ;  it  receives  blood  from  the  hippocampus 
major,  the  fornix,  and  the  corpus  callosum. 

The  vein  of  the  septum  lucidum,  a  long,  slender  vessel, 
receives  blood  from  the  septum  lucidum,  the  anterior  part  of 
the  corpus  callosum,  and  the  corresponding  part  of  the  lateral 
ventricle,  and  extends  downward  to  join  the  vein  of  Galen  near 
the  foramen  of  Monro. 

Each  vein  of  Galen  runs  backward,  parallel  with  its  fellow, 
between  the  layers  of  the  velum  interpositum,  and  passes  out  of 
the  brain  through  the  transverse  fissure,  there  joining  its  fellow 
to  form  a  single  trunk,  the  great  vein  of  Galen,  which  enters  the 
straight  sinus. 


VEINS  OF  THE  CEREBELLUM. 

The  blood  of  the  cerebellum  is  collected  by  two  systems — the 
superior  and  inferior  cerebellar  veins.  The  superior  cerebellar 
veins,  which  are  distributed  over  the  upper  surface  of  the  cere- 


BLOOD-VESSELS    OF    THE   BRAIN. 


441 


bellum,  collect  their  blood  from  the  surface  to  pass  forward  and 
inward  over  the  surface  of  the  superior  vermis  to  empty,  some 
in  the  straight  sinus,  others  into  the  vein  of  Galen. 

The  inferior  cerebellar  veins,  which  are  distributed  over  the 


Ant.' facial  vein 


Ext.  jugul  vein 


Communication  with  veins 
nt  back  of  neck 


Fig.  217. — Diagram  Showing  Communications  Existing  Between  the  Lateral  and 
Cavernous  Sinuses  and  the  External  Veins,  Indicated  in  Figure  by  *. — 
(yAfter  Leube.) — {Fro?n  Looinis  and  Thompson,  "  Practice  of  Medicine.^') 

under  surface  of  the  cerebellum,  collect  their  blood  from  that 
surface  and  pass  forward  and  outward  to  empty,  some  into  the 
inferior  petrosal  and  lateral  sinuses,  while  others  pass  backward 
to  the  occipital  sinuses. 


442  CENTRAL  NERVOUS  SYSTEM. 

THE  VENOUS  SIXUSES. 

The  venous  spaces  ot  the  cranium  are  inclosed  between  the 
two  layers  of  the  dura  mater  which  form  their  walls,  and  are 
lined  with  endothelium  continuous  with  that  lining  the  veins 
which  empty  into  them.  They  have  extending-  across  their 
lumen  numerous  rather  firm  bands  of  connective  tissue,  w'hich 
in  some  of  the  spaces  are  arranged  in  a  cavernous  manner. 
These  sinuses  are,  with  but  few  exceptions,  long,  capacious 
channels,  which  collect  blood  from  tlie  various  veins  of  the  brain, 
and  from  some  of  the  veins  of  the  diploe,  and  carry  it  chiefly  to 
the  internal  jugular  vein.  They  are  connected  with  the  superfi- 
cial veins  of  the  external  surface  of  the  cranium  by  several 
emissary  veins,  which  pass  through  foramina  of  the  cranial 
bones.  There  are  sixteen  cranial  sinuses,  six  of  which  are 
single  and  are  placed  in  the  median  line,  and  five  are  arranged 
in  pairs,  one  for  each  side.  The  single  sinuses  are  the  superior 
longitudinal,  the  inferior  longitudinal,  the  straight,  the  occipital, 
the  circular,  and  the  transverse.  The  paired  sinuses  are  the 
lateral,  the  superior  petrosal,  the  inferior  petrosal,  the  cavern- 
ous, and  the  sphenoparietal. 

The  superior  longitudinal  sinus  (sagittal  or  falciform  sinus) 
extends  in  a  curved  manner  from  the  foramen  caecum  to  the  in- 
ternal occipital  protuberance,  occupying  the  attached  margins 
of  the  falx  cerebri.  It  is  lodged  in  a  median  groove  along  the 
under  surface  of  the  calvarium.  This  sinus  increases  in  size  from 
before  backward,  and  presents  on  transverse  section  a  trian 
gular  appearance.  Its  lumen  is  crossed  by  several  fibrous  bands, 
and  has  projecting  into  it  several  Pacchionian  bodies.  The 
sinus  terminates  in  the  right  lateral  sinus,  at  the  internal  occipi- 
tal protuberance,  in  a  dilatation  called  the  sinus  confluens,  or  the 
torcular  Herophili.  Into  this  sinus  empty  the  superior  veins  of 
the  external  and  median  surfaces  of  the  convolutions,  as  well  as 
a  few  from  the  basal  surface,  and  numerous  small  veins  from 
the  diploe  and  dura  mater.  The  middle  meningeal  veins  often 
end  in  small  diverticuli  in  the  dura  mater, — lacunae  venosa;  lat- 
erales, — which  communicate  with  the  veins  of  the  diploe.  Ac- 
cording to  Trolard,  these  spaces  act  as  compensating  reservoirs 


BLOOD-VESSELS    OF    THE   BRAIN.  443 

whenever,  owing  to  any  temporary  obstruction  to  the  circula- 
tion, the  sinuses  are  overdistended,  the  blood  passing  from  the 
spaces  into  the  veins  of  the  diploe  and  thence  into  the  pericra- 
nial veins.  An  emissary  vein  enters  this  sinus  from  the  peri- 
cranium through  the  parietal  foramen,  and  in  fetal  life  this  sinus 
communicates  through  the  foramen  csecum  with  the  nasal  veins. 
The  superior  longitudinal  sinus  is  in  connection  with  the  cav- 
ernous or  superior  petrosal  sinuses  by  the  great  anastomotic 
vein  of  Trolard. 

The  inferior  longitudinal  sinus,  also  called  the  falciform  vein, 
is  located  in  the  concave  border  of  the  inferior  surface  of  the 
falx  cerebri.  It  begins  about  the  junction  of  the  anterior  with 
the  middle  third  of  the  falx  cerebri,  and  extends  backward  in 
a  curved  manner  to  the  point  of  union  of  the  falx  cerebri  with 
the  tentorium  cerebelli,  where  it  terminates  in  the  straight  sinus. 
It  collects  blood  from  some  of  the  descending  veins  of  the 
median  surface  of  the  hemispheres,  as  well  as  a  few  from  the 
falx  cerebri. 

The  Straight  Sinus. — The  straight  sinus  is  located  along 
the  line  of  junction  of  the  falx  cerebri  with  the  falx  cerebelli, 
and  is  formed  by  the  union  of  the  inferior  longitudinal  sinus 
with  the  vein  of  Galen.  It  pursues  an  oblique  course  from 
above  downward  and  backward,  receiving  in  its  course  tributa- 
ries from  the  superior  surface  of  the  cerebellum  and  from  the 
tentorium  cerebelli,  and  usually  terminates  in  the  left  lateral 
sinus  or  in  the  torcular  Herophili.  Rarely,  the  straight  sinus 
has  the  occipital  sinus  emptying  into  it. 

The  Occipital  Sinus. — The  occipital  sinus  originates  in  two 
branches, — the  so-called  marginal  sinuses, — one  for  each  side, 
which,  taking  their  origin  from  the  termination  of  the  lateral 
sinuses,  course  along  the  foramen  magnum,  and  communicating 
with  the  posterior  spinal  veins,  unite  close  to  the  internal  occipi- 
tal protuberance  in  a  single  trunk,  the  occipital  sinus.  This 
sinus  is  situated  alono-  the  attached  margins  of  the  falx  cerebelli, 
and  after  a  short  course  backward,  terminates  either  in  one  of 
the  lateral  sinuses,  the  torcular  Herophili,  or  rarely  in  the 
straight  sinus.  It  receives  branches  from  the  tentorium  cere- 
belli and  from  the  inferior  surface  of  the  cerebellum,  and  it  com- 


444 


CENTRAL  NERVOUS  SVSTKM. 


municates  through  the  anterior  condyloid  foramen,  by  means  of 
a  venous  plexus  which  surrounds  the  hypoglossal  nerve,  with  the 
vertebral  vein  and  with  the  anterior  spinal  plexus. 

The  Circular  Sinus. — The  circular  sinus  is  formed  by  two 
transverse  vessels  which  connect  the  cavernous  sinuses,  and  are 
placed  one  in   front  and  the  other  behind  the  pituitary  body, 


Fig.  2iS. — Mf.disection  of  Brain,  showing  Important  Sinuses. 
I.  Falx  cerebri.  2,  2.  Its  convex  border,  with  the  great  longitudinal  sinus.  3.  Its  concave 
border.  4,  4.  Inferior  longitudinal  sinus.  5.  Base  of  falx  cerebri.  6.  Straight  sinus. 
7.  Apex  of  falx  cerebri.  8.  Right  half  of  the  tentorium,  seen  from  below.  9.  Right 
lateral  sinus.  10.  Superior  petrosal  sinus.  11.  Inferior  petrosal  sinus.  12.  Posterior 
occipital  sinus.  13.  Falx  cerebelli.  14.  Optic  nerve.  15.  Motor  oculi.  16.  Pathetic. 
17.  Trigeminus.  18.  Abducens.  19.  Facial  and  auditory  nerves.  20.  Glossopharyngeal, 
pneumogastric,  and  spinal  accessory  nerves.  21.  Hypoglossal  nerve.  22.  First  cervical 
nerve.      23.   Second  cervical  nerve.      24,  24.   Upper  extremity  of  ligamentum  denticulatum. 

or    hypophysis    cerebri,    forming    a    venous    circle   about   that 
body. 

The  Transverse  or  Basilar  Sinus. — The  transverse  sinus 
consists  of  a  venous  plexus  between  the  layers  of  the  dura 
mater  over  the  basilar  process  of  the  occipital  bone.  It  has  a 
transverse  course  between  the  two  Inferior  petrosal  sinuses, 
which  It  connects. 


',  ^--^A^,.--  BLOOD-VESSELS    OF    THE   BRAIN.  445 

""^^^hG  Lateral  Sinuses. — The  riorht  and  left  lateral  sinuses 
are  the  very  voluminous  venous  channels  located  between  the 
layers  of  the  tentorium  cerebelli.  They  communicate  at  the 
internal  occipital  protuberance,  the  right  usually  being  the  con- 
tinuation of  the  superior  longitudinal  sinus,  while  the  left  is  a 
continuation  of  the  straight  sinus.  Both  increase  in  size  as 
they  proceed  outward  and  forward,  terminating  by  passing 
downward  and  inward  to  the  jugular  foramen,  where  they  be- 
come continuous  with  the  sinus  jugularis  or  bulb  of  the  internal 
jugular  vein.  These  sinuses  rest  in  a  groove  located  on  the 
inner  surface  of  the  occipital,  the  postero-inferior  surface  of  the 
parietal,  the  mastoid  portion  of  the  temporal,  and  the  jugular 
process  of  the  occipital  bones.  These  sinuses  collect  blood 
from  some  of  the  inferior  cerebral  and  cerebellar  veins,  as  well 
as  from  some  of  the  veins  of  the  pons  Varolii  and  medulla.  They 
communicate  with  the  veins  of  the  pericranium  by  means  of 
emissary  veins  through  the  mastoid  and  posterior  condyloid 
foramina,  and  have  emptying  into  them  the  superior  petrosal 
sinuses. 

The  Superior  Petrosal  Sinuses. — The  superior  petrosal 
sinuses  are  situated  at  the  attached  mareins  of  the  tentorium 
cerebelli,  along  the  superior  border  of  the  petrous  portion  of 
each  temporal  bone.  They  connect  the  cavernous  with  the 
lateral  sinuses.  In  their  course  from  the  cavernous  to  the  lat- 
eral sinus,  crossing  the  fifth  pair  of  cranial  nerves,  they  receive 
some  of  the  inferior  cerebral  veins,  and  veins  from  the  inner 
ear.  They  are  sometimes  connected  with  the  superior  longitu- 
dinal sinus  by  means  of  the  great  anastomotic  vein  of  Trolard. 

The  Inferior  Petrosal  Sinuses. — The  inferior  petrosal 
sinuses  are  shorter  but  wider  channels  than  the  superior  petro- 
sal sinuses,  and  are  located  in  a  groove  formed  by  the  junction 
of  the  petrous  portion  of  the  temporal  bone  with  the  basilar 
portion  of  the  occipital  bones.  They  connect  the  cavernous 
sinuses  with  the  beginning  of  the  internal  jugular  veins.  As 
they  course  across  each  jugular  foramen,  they  separate  the 
glossopharyngeal  from  the  pneumogastric  and  spinal  accessory 
nerves.  They  receive  veins  from  the  inferior  surface  of  the 
cerebellum,  from  the  pons  and  medulla,  and  from  the  middle  ear. 


446 


CENTRAL  NKRVOUS  SYSTEM. 


The  Cavernous  Sinuses. —  The  cavernous  sinuses,  two  in 
number,  are  very  capacious  and  irregularly  shaped  blood-spaces 
located  between  the  layers  of  the  dura  mater  and  extending 
backward  from  the  inner  opening  of  the  sphenoid  fissure  to 
the  apex  of  the  petrous  portion  of  the  temporal  bone,  where 
they  open  into  the  superior  and  inferior  petrosal  sinuses.  In 
front  they  are  continuous  with  the  ophthalmic  veins  and  also 
receive  the  sphenoparietal  sinuses  and  some  of  the  inferior 
cerebral  veins.  They  communicate  with  each  other  by  means 
of  the  circular  sinuses,  and  are  usually  connected  on  each  side 
with  the  superior  longitudinal  sinus  by  means  of  the  great 
anastomotic  vein  of  Trolard. 

These  sinuses  are  traversed  by  numerous,  mostly  transversely 
arranged,  fibrous  bands,  which  divide  the  sinuses  into  a  number 


Lining  membrane  of  sinus. 


Dura  maler  lining 
pituitary  fossa 


on  of  fifth  nerve. 


Fig.  219.— Plan  Showing  thk  Relative  Position  of  the  Structures  in  the  Right 
Cavernous  Sinus,  Viewed  from  Behind. — {A//cr  Gray.) 


of  lacunar  lined  by  endothelium.  \'on  Langer  has  shown  that 
the  cavernous  sinuses  were  originally  a  plexiform  network  of 
veins,  which,  by  the  gradual  fusion  of  their  channels,  produce 
the  characteristic  lacunar  appearance.  The  internal  carotid 
artery  and  the  sixth  cranial  nerve  are  located  along  the  inner 
wall  of  this  sinus,  while  along  the  outer  wall  run  the  third, 
fourth,  and  the  ophthalmic  division  of  the  fifth  cranial  nerves, 
all  these  structures  being  separated  from  the  blood  within  the 
sinus  by  the  lining  membrane  of  the  sinus. 

The  Sphenoparietal  Sinus. — Each  sphenoparietal  sinus 
originates  near  the  apex  of  the  lesser  wing  of  the  sphenoid 
bone,  in  one  of  the  meningeal  veins,  and,  passing  in  a  groove  on 
the  under  surface  of  the  lesser  wing  of  the  sphenoid  bone,  ex- 


BLOOD-VESSELS    OF    THE   BRAIN.  447 

tends  inward  through  a  fold  of  the  dura  mater  above  the  third 
nerve,  to  reach  the  cavernous  sinus,  with  which  it  is  continuous. 


THE  EMISSARY  VEINS. 

The  following  important  emissary  veins  connect  the  venous 
sinuses  with  the  extra  cranial  veins : 

1.  A  vein,  almost  constant,  passing  from  the  lateral  sinus 
through  the  mastoid  foramen,  empties  into  the  occipital,  post- 
auricular,  or  external  jugular  veins. 

2.  The  ophthalmic  vein  passes  backward  through  the  orbital 
fissure,  emptying  into  the  cavernous  sinus,  thus  establishing  a 
connection  between  that  sinus  and  the  veins  of  the  eyeball  and 
orbit,  as  well  as  with  the  veins  of  the  anterior  portion  of  the 
scalp. 

3.  A  vein  passing  through  the  parietal  foramen  and  connect- 
ing the  superior  longitudinal  sinus  with  the  veins  of  the  scalp 
of  the  parietal  region. 

4.  A  minute  plexus  of  veins  which  pass  through  the  anterior 
condyloid  foramen,  connecting  the  occipital  sinus  with  the  ver- 
tebral veins  and  the  deep  veins  of  the  neck. 

5.  The  posterior  jugular  vein,  passing  through  the  posterior 
condyloid  foramen,  connects  the  lateral  sinus  with  the  upper 
cervical  or  vertebral  veins. 

6.  A  rather  large  vein  which  passes  through  the  foramen 
ovale  and  connects  the  cavernous  sinus  with  the  pharyngeal 
plexus. 

7.  A  plexus  of  veins  in  the  carotid  canal  connects  the  cavern- 
ous sinus  with  the  internal  jugular  vein. 


CHAPTKR  XII. 

CEREBRAL  LOCALIZATION. 

Probably  the  most  important  subject  from  a  clinical  and  scien- 
tific standpoint,  in  connection  with  the  nervous  system,  is  the 
question  of  cerebral  localization — /.  c,  that  certain  known  areas 
of  the  brain  preside  over  certain  definite  functions  ;  and  while 
not  strictly  a  part  of  anatomy,  its  importance  justifies  its  intro- 
duction here. 

For  many  years  it  has  been  generally  known  that  each  cere- 
bral hemisphere  is  in  functional  relation  with  the  opposite  side 
of  the  body,  and  even  the  discoveries  of  Thomas  Hood  in  Eng- 
land and  Bouillaud  in  France,  that  in  several  cases  of  speech- 
defect  the  frontal  lobes  were  found  affected,  excited  no  general 
interest,  since  the  doctrine  of  Flourens — namely,  that  while  the 
brain  was  the  seat  of  the  higher  mental  faculties,  they  were  not 
localizable,  but  evenly  distributed  throughout,  and  the  brain 
acted  as  a  whole — was  commonly  accepted. 

The  publication,  however,  in  1861,  by  Broca,  of  several  cases 
of  aphasia  with  autopsies,  which  enabled  him,  owing  to  the  con- 
stant relation  between  the  form  of  speech-defect  and  the  lesion, 
to  positively  locate  the  motor  speech-center  in  the  left  inferior 
frontal  gyrus,  was  the  starting-point  of  the  study  of  cerebral 
localization.  Shortly  after,  Hughlings  Jackson,  of  London,  re- 
corded a  number  of  cases  in  which  partial  or  complete  unilateral 
convulsions  had  occurred,  the  autopsies  showing  that  certain 
circumscribed  areas  of  the  brain  were  found  uniformly  affected, 
thus  proving  the  connection  between  irritation  of  certain  areas 
of  the  brain  and  local  convulsive  movements. 

The  observations  of  Broca  and  Jackson,  together  with  the 
publication    of    the    experimental    researches    of    Fritsch    and 

Hitzig,  of  Berlin,  in   1870,  of  Ferrier   in    1873,  ^^<^  of  Monk   in 

44S 


CEREBRAL  LOCALIZATION. 


449 


1 88 1,  completely  disproved  the  hitherto  accepted  conclusion  of 
Flourens  and  opened  the  way  to  a  series  of  brilliant  discoveries 
which  have  established  cerebral  localization  upon  a  scientific 
basis. 

Although  there  is  still  some  difference  of  opinion  among  in- 
vestig-ators  as  to  the  absolute  limits  of  certain  localizable  areas, 
it  is  settled  beyond  dispute  that  there  are  fixed  areas  presiding 
over  motion,  language,  and  sight,  and  a  strong  presumption  in 
favor  of  the  localization  of  the  various  forms  of  common  sensa- 
tion, of  most  of  the  special  senses,  and  of  the  higher  intellectual 
faculties. 

In   the   cerebral   cortex  there   are  localized  areas  governing 


Fig.  220. — Diagram  of  the  Motor  Areas  on  the  Outer  Surface  of  a   Monkey's 
Brain. — {^Horsley  and  Schdfer,  from  Landois  a?id  Stirling.^ 


motion,  common  sensation,  the  special  senses  of  sight,  hearing, 
taste  and  smell,  speech  processes,  and  the  higher  mental  faculties. 
The  cortical  area  governing  motion,  known  as  the  motor  area 
of  the  brain,  is  a  large  district  of  the  cerebral  cortex,  lying  on 
each  side  of  the  fissure  of  Rolando,  between  the  precentral  and 
intraparietal  fissures.  It  comprises  the  posterior  part  of  the 
inferior  or  third  frontal  gyrus,  the  ascending  frontal  and  parietal, 
or,  as  they  are  often  termed,  the  pre-  and  postcentral  gyri,  and 
their  junction  on  the  mesial  surface  of  the  hemisphere,  the  para- 
central lobule.  To  this  may  be  added  the  posterior  part  of  the 
superior  and  middle  frontal  gyri  and  a  part  of  the  superior 
parietal  lobule.     The  axones  from  the  large  pyramidal  cells  of 

this  extensive  area  form  the  great  motor  tract,  the  course  of 

29 


450 


CENTRAL  NERVOUS  SYSTEM. 


which  through  the  centrum  semiovale,  internal  capsule,  crus 
cerebri,  pons,  medulla,  and  spinal  cord  has  been  thoroughly 
discussed.  It  is  by  means  of  this  tract  that  impulses  of  volun- 
tar\-  motion  originating  in  this  area  are  conducted  to  the  mus- 
cles of  the  opposite  side  of  the  body,  resulting  in  coordinated 
movements.  Clinic,  pathologic,  and  experimental  studies  have 
established  beyond  dispute  the  fact  that  destructive  lesions  of 
this  area  produce  paralysis  on  the  opposite  side  of  the  bod\-, 
with  a  resultinor  descendinij  degreneration  of  the  entire  cortico- 
spinal  part  of  the  motor  tract  coming  from  that  side,  while  irri- 
tative lesions  cause  unilateral  convulsions  of  the  opposite  side. 
The  further  subdivision  of  this  area  into  centers  for  the  inner- 


FlG.   221. — DI.A.GRAM    OF    THE    MOTOR    AREAS    ON    THE    MARGINAL   CONVOLUTION    OK   A 

Monkey's  Brain. — {Horsley  and  Schdfer,  from  Landois  and  Stirling.) 


vation  of  the  muscles  for  the  trunk,  leg,  arm,  face,  and  head  has 
been  established  by  the  study  of  partial  or  complete  unilateral 
spasms,  the  results  of  circumscribed  electric  excitation  of  the 
cortex  in  the  lower  animals,  and  by  clinic  and  pathologic  obser- 
vations on  man. 

To  Fritsch  and  Hitzie  belongs  the  credit  of  first  havincj  estab- 
lished  the  fact  that  the  application  of  the  galvanic  current  to 
certain  areas  on  the  surface  of  the  doe's  brain  o-ives  rise  to  co- 
ordinated  movements  in  distinct  groups  of  muscles  of  the  oppo- 
site side  of  the  body,  while  stimulation  elsewhere  produces  no 
result.  These  observations  were  not  only  verified,  but  further 
extended  by  Ferrier,  whose  experiments  were  mostly  on  the 
brains  of  monkeys.      He  was  able  not  only  to  locate  in   a  gen- 


CEREBRAL  LOCALIZATION. 


451 


eral  way  the  motor  region,  and  by  electric  stimulation  of  certain 
small  areas  to  map  out  separate  centers  for  the  movements  of 
the  leg,  arm,  face,  and  head,  but  he  also  showed  that  electric 
irritation  of  most  of  the  prefrontal  region,  the  temporal,  occipi- 
tal, and  parts  of  the  parietal  lobe,  was  unattended  by  muscular 
movements,  proving  that  these  areas  are  not  motor  in  function. 
More  recently  Ferrier's  observations  have  been  confirmed  and 
other  facts  of  interest  have  been  added  to  our  knowledoe  of 
localization  through  the  efforts  of  Horsley,  Schafer,  and  Beevor. 
The  delineation  of  the  various  subdivisions  of  the  motor  region 
in  man  has  resulted  from  the  study  of  a  large  number  of  care- 


FiG.  222.— A  Drawing  of  the  Left   Cerebral  Hemisphere  (Human) 
different  localizable  areas  on  the  external  surface. 


Showing  the 


fully  reported  cases  with  autopsies,  and  by  the  careful  electric 
excitation  of  circumscribed  areas  of  the  cortex  during  its  expo- 
sure for  cerebral  operations.  In  the  main,  these  areas  in  man 
correspond  with  those  located  by  Ferrier  and  others  on  the  sur- 
face of  the  brain  of  monkeys.  In  a  general  way  it  may  be 
stated  that  the  leg  area  occupies  the  upper  third,  the  arm  area 
the  middle  third,  and  \ki^  face  area  the  lower  third  of  the  motor 
region,  or  the  ascending  frontal  and  parietal  gyri ;  while  the 
trunk-muscles  are  chiefly  represented  on  the  median  surface  of 
these  two  gyri,  the  paracentral  lobule.  Monk,  however,  places 
the  area  for  the  trunk  muscles  in  the  prefrontal  lobe. 


452 


CENTRAL  NERVOUS  SYSTEM. 


The  leg  area  occupies  the  upper  third  of  the  central  gyri,  the 
posterior  part  of  the  paracentral  lobule,  and  the  upper  anterior 
part  of  the  superior  parietal  lobule.  Thus  it  occupies  a  greater 
anteroposterior  surface  than  does  the  area  of  the  arm  or  of 
the  face.  It  consists  of  a  series  of  centers,  arranged  from  be- 
fore backward,  for  the  muscles  governing  the  movements  ot  the 
thigh,  knee,  foot,  and  toes. 

The  arm  area,  which  occupies  the  middle  third  ot  the  central 
gyri,  is  subdivided  from  above  downward  into  centers  tor  the 
movements  of  the  shoulder,  elbow,  hand,  and  lingers.  The 
center  which  presides  over  movements  ot  the  shoulder  exists  in 


Fig.  223. — A  Drawing  of  thk  Right  Cekebr.\l  Hemisphere  (Human).     Showing 
localizable  areas  on  the  median  surface. 


the  upper  part  of  this  area,  and  a/so  in  ike  anto'ior  part  of  the 
paracentral  lobule.  The  center  for  the  elbow  is  in  the  middle 
part  of  this  area,  and  the  centers  for  the  hand  and  fingers  are  in 
the  lower  part. 

The  face  area  is  located  in  the  lower  third  of  the  ascending 
frontal  and  ascending  parietal  convolutions.  It  consists  of  two 
portions,  an  upper  and  a  lower,  for  the  corresponding  facial  mus- 
cles. In  the  upper  part  are  centers  for  the  orbicularis  palpe- 
brarum and  occipitofrontalis  muscles,  and  in  the  lower  part,  for 
the  muscles  of  the  lips,  tongue,  pharynx,  and  larynx. 

The  studies  of  Semon  and  Horsley,  and  the  cases  of  Seguin 
and  Dejerine,  seem  to  prove  the  existence  of  a  separate  center 


CEREBRAL  LOCALIZATION. 


45: 


for  the  laryngeal  muscles  in  the  inferior  part  of  the  ascending 
and  the  root  of  the  inferior  or  third  frontal  gyrus.* 

There  probably  exists  a  separate  center  on  each  side  for  the 
elevation  of  the  eyelids,  through  the  action  of  the  levator  pal- 
pebrae  superioris  muscle.  This  center,  according  to  Ferrier, 
Horsley,  and  Mott,  is  in  the  posterior  part  of  the  second  frontal 
gyrus.  In  a  few  cases  of  ptosis,  however,  which  have  come  to 
autopsy,  lesions  have  been  found  in  the  angular  gyrus.  These 
were  probably  cases  of  reflex  paralysis,  the  result  of  the  lesion, 
from  a  failure  to  respond  to-visual  excitations. 

The  cortical  area  for  the  muscles  of  the  trunk  and  spine  is  a 
small  part  of  the  ascending  frontal  gyrus,  close  to  the  longitu- 
dinal sinus,  and  the  part  of  the  paracentral  lobule  located  be- 


FiG.    224. — Position    of    the    Arm. — 
i^Afler  Goweis.) 


Fig.  225. — Position  of  the  Center 
for  the  Face  and  Tongue.— (^/^'^t 
Goweis. ) 


tween  the  centers  for  the  leg  and  shoulder  muscles.  The  exact 
position  of  the  centers  governing  the  movements  of  the  head 
and  eyes  is  not  positively  known.  Their  probable  location  is 
in  the  posterior  part  of  the  first  and  second  frontal  gyri  adjacent 
to  the  ascending  frontal,  and  on  the  mesial  surface  of  the  first 
frontal  convolution. 

Ferrier  has  proved,  from  the  results  of  electric  stimulation 
of  the  inferior  part  of  the  postcentral  gyrus  of  the  brain  of  a 
monkey,  that  a  center  exists  there  for  the  retraction  of  the  angle 
of  the  mouth.  Bramwell  has  recorded  an  interestine  case,  in 
confirmation  of  Ferrier's  belief,  of  a  woman  who  frequently  had 


*  Herter  has  reported  a  case  of  left-sided  ptosis,  with  slight  dilatation  of  the  left  pupil  and 
with  paresis  of  the  right  arm  and  leg.  The  autopsy  disclosed  an  area  of  softening  one  inch  in 
diameter  confined  to  the  right  angular  gyrus.  The  right  hemiparesis,  he  believed,  was  due  to 
uremia. 


454  CENTRAL  NERVOUS  SYSTEM. 

convulsions,  whicli  always  began  in,  and  were  often  confined  to, 
the  right  platysma  myoides  muscle,  in  which  case  a  spicula  of 
bone  was  found  irritating  the  inferior  margin  of  the  postct-ntral 
gyrus.  It  must  be  remembered  that  while  different  areas  exist 
for  the  innervation  of  the  muscles  of  the  trunk,  leg,  arm,  and  face, 
these  areas  are  not  sharply  separated,  but  blend  or  interdigitate 
with  one  another. 

The  study  of  autopsies  following  cases  of  partial  unilateral 
convulsions  has  proved  that  these  centers  exist  only  in  the 
cortex.  In  that  peculiar  type  of  convulsion  first  described  by 
Jackson,  and  from  him  called  Jacksonian  epilepsy,  the  initial 
symptom  is  always  a  spasm  limited  to  a  definite  group  of  mus- 
cles, followed  by  a  convulsion,  more  or  less  complete,  of  the 
same  side,  successive  groups  of  muscles  being  involved  in  regu- 
lar order.  On  section,  the  lesion  has  been  found  to  be  located 
in  the  opposite  cerebral  hemisphere,  in  the  center  presiding  over 
the  group  of  muscles  in  which  .the  spasm  started,  and  either  in 
the  cortex  or  in  such  a  manner  as  to  affect  the  cortex  by  pres- 
sure. Several  recorded  cases  of  recent  date  would  seem  to 
prove,  however,  that  Jacksonian  attacks  may  be  produced  by 
lesions  of  slow  o-rowth  which  irritate  the  motor  tract  below  the 
cortex. 


THE  CORTICAL  CENTERS  FOR  GENERAL 
SENSATIONS. 

There  is  at  present  considerable  disagreement  among  experi- 
mental physiologists  with  regard  to  the  exact  location  in  the 
cerebral  cortex  of  the  centers  for  the  reception  of  the  various 
forms  of  sensory  impressions  from  the  skin,  mucous  membranes, 
joints,  and  muscles.  Ferrier  believes  that  in  the  brain  of  the 
monkey,  and  hence  presumably  in  man,  these  centers  are  located 
in  the  cortex  of  the  gyrus  fornicatus  and  hippocampal  gyrus.* 

*  Charles  K.  Mills  maintains,  with  Ferrier,  that  the  receptive  centers  for  general  sensation 
are  located  in  the  cortex  of  the  fornicate  and  hippocampal  gyri.  In  support  of  his  belief  he 
refers  to  two  cases  reported  by  Saville,  in  both  of  which  there  was  a  loss  of  tactile  sense  conse- 
quent upon  lesions  of  the  fornicate  gyrus  and  the  underlying  white  matter.  It  seems  to  me, 
judging  from  the  experience  of  von  Monakow,  that  what  is  most  needful  to  prove  the  existence 
of  separate  sensory  centers  in  this  region  is  to  find  the  lemniscus  degenerated,  following  such 
lesions.     Of  this  no  mention  is  made. 


CEREBRAL  LOCALIZATION.  455 

He  bases  his  belief  on  the  results  of  a  number  of  experiments 
on  monkeys,  in  which,  after  destruction  of  these  areas,  par- 
tial or  complete  loss  of  the  various  forms  of  general  sensation 
occurred  in  the  limbs  of  the  opposite  side  of  the  body.  He  was 
careful  in  his  experiments  not  to  interfere  with  the  integrity  of 
the  internal  capsule  or  with  the  sensory  cortical  radiations  from 
the  capsule.  He  does  not  believe  that  the  region  bordering 
upon  the  fissure  of  Rolando  (motor  area)  is  concerned  in  the 
reception  of  sensory  impressions,  its  only  function  being  the 
excitation  of  motor  impulses.  While  the  results  reached  by 
Ferrier  as  to  the  location  of  the  sensory  centers  seem  conclusive, 
still  they  lack  the  support  of  many  physiologists.  Hitzig,  Munk, 
Luciani,  Horsley,  and  Mott  seem  to  be  in  accord  in  locating  the 
sensory  centers  in  the  region  bordering  on  the  fissure  of  Rolando 
— that  is,  in  the  motor  area  ;  and,  according  to  these  observers, 
this  region  is  both  motor  and  sensory  in  function,  hence  properly 
termed  the  sensorimotor  area.  They  operated  by  either  partially 
or  totally  extirpating  from  the  brains  of  monkeys  the  various 
areas  of  this  region,  or  by  separating  these  areas  from  their 
nerve  connections.  They  found  that  after  such  operations  there 
was  invariably  induced  paralysis,  both  of  motion  and  sensation, 
in  the  limbs  of  the  opposite  side  of  the  body  ;  the  extent  of  the 
loss  depending  upon  the  extent  of  the  lesion.  They  also  ob- 
served that  if  small  areas  of  the  motor  region  were  destroyed, 
while  both  motor  and  sensory  paralysis  resulted,  the  former  was 
nearly  always  permanent,  whereas  the  latter  would  gradually  and 
completely  disappear.  This  Mott  explains  by  the  difference  in 
the  anatomic  arrangement  of  the  motor  and  sensory  fibers  ; 
the  former — originating  from  the  motor  cells,  which  are  their 
trophic  centers — being  destroyed  close  to  their  origin,  there  re- 
sults a  complete  disintegration  of  these  fibers,  with  a  corre- 
sponding permanent  loss  of  function  ;  whereas  in  the  case  of  the 
latter,  or  sensory  fibers, — which  are  on  their  way  to  the  cerebral 
cortex,  where  they  terminate,  after  having  given  ofi"  collaterals, 
by  spreading  out  into  cortical  arborizations  which  occupy  a  large 
extent  of  surface, — it  is  perfectly  conceivable  that  a  small  circum- 
scribed lesion  can   not  completely  destroy  the  collaterals  and 


456  CENTRAL  NERVOUS  SYSTEM. 

arborizations  of  the  terminal  fiber  and  the  remainini^  branches 
quickly  take  up  the  function  of  the  whole. 

In  confirmation  ot  the  views  of  the  above-mentioned  physi- 
ologists, that  the  motor  area  is  also  sensory  in  function, — destruc- 
tion producing,  in  addition  to  motor  paralysis,  partial  or  com- 
plete loss  of  sensation  in  the  opposite  side  of  the  body, — comes 
the  collection  of  a  large  number  of  carefully  recorded  cases 
with  autopsies.  This  has  been  accomplished  through  the  labors 
of  Horsley,  Gowers,  W'estphal,  Dejerine,  Seguin,  Dana,  and 
Starr,  Dana's  twenty-five  cases,  twenty-one  from  literature  and 
four  personal,  all  prove  that  lesions  of  the  central  convolutions 
are  attended  by  partial  or  complete  loss  of  tactile,  temperature, 
pain,  and  muscular  senses  in  the  limbs  of  the  opposite  side  of 
the   body. 

Horsley  found  undoubted  sensory  defects  after  extirpating  in 
man  a  large  area  of  the  motor  region.  He  is  of  the  opinion 
that  the  two  outer  layers  of  the  pyramidal  cells  of  the  cortex 
are  concerned  in  the  impressions  of  tactile  and  muscular  sense, 
while  the  deepest  layer,  or  layer  of  large  pyramidal  cells,  origi- 
nates motor  impulses. 

Allen  Starr,  from  an  experience  of  thirty  cases  of  cerebral 
operations  on  man,  consisting  of  excisions  of  parts  of  the 
motor  area,  thinks  that  it  is  clearly  determined  that  the  tac- 
tile centers  are  situated  in  the  Rolandic  area,  especially  in  the 
postcentral  gyrus.  He  also  relates  an  interesting  case  in  con- 
firmation of  his  belief  that  the  cortical  area  for  the  reception 
of  muscular  sense  impressions  is  in  the  posterior  central  and 
inferior  parietal  lobules.  The  patient  had  a  bolt  driven  through 
the  left  parietal  bone  over  the  position  of  the  hand  area,  which 
produced  paralysis  of  the  hand  and  arm,  with  but  slight  impair- 
ment of  tactile,  pain,  and  temperature  sense,  but  with  marked 
impairment  of  muscular  sense.  At  the  operation  for  elevating 
the  depressed  portion  of  the  skull  an  extensive  injury  to  the 
parietal  cortex  was  found,  with  an  abscess  beneath  the  depressed 
bone.  In  addition  to  the  know^ledge  gained  by  experimental 
and  clinicopathologic  observations  in  regard  to  the  sensory 
centers  of  the  cortex  comes  the  evidence  from  the  embryologic 


CEREBRAL  LOCALIZATION.  457 

Studies  of  the  sensory  tract  by  Flechsig  and  Edinger,  and  from 
the  study  of  secondary  degeneration  by  von  Monakow,  both  of 
which  methods  bring  the  same  conclusion — viz.,  that  the  sensory 
fibers  ("fillet"  or  "  lemniscus  ")  terminate  in  the  cortex  of  the 
postcentral  convolution  and  parietal  lobe.*  Hence  the  gener- 
ally accepted  conclusion  in  regard  to  the  location  of  both  motor 
and  sensory  centers  in  man  is  that  they  occupy  in  common  the 
region  about  the  fissure  of  Rolando. 

Nothnagel,  Luciani,  Seppelli,  and  Flechsig  long  ago  asserted 
that  the  parietal  lobes  were  concerned  in  the  reception  of  mus- 
cle sense  impressions,  and  possibly  of  the  other  forms  of  gen- 
eral sensations. 

Redlich,  from  an  analysis  of  twenty  cases  of  lesions  confined 
to  the  parietal  lobes,  states  positively  that  these  lobes  are  the 
centers  for  muscle  sense. 

In  a  recent  case  of  von  Monakow's,  of  a  lesion  involving  the 
white  substance  of  the  angular  and  supramarginal  gyri,  there  was 
a  marked  disturbance  of  the  muscle  sense,  without  the  slightest 
paresis.  A  microscopic  examination  of  the  central  convolutions 
and  the  white   matter   beneath  them  elicited  nothing  abnormal. 

Von  Vetter  reports  a  case  of  a  woman  with  decided  ataxia  of 
the  extremities  of  the  left  side,  without  the  slightest  disturbance 
of  motion,  in  which  a  lesion  the  size  of  an  apple  was  found 
located  in  the  parietal  lobes  ;  the  central  convolutions  were 
normal. 


THE  CENTERS  OF  VISION. 

There  seems  to  be  a  unanimity  of  opinion  among  physiolo- 
gists and  clinicians  that  the  visual  centers  are  located  in  the 
occipital  lobes,  chiefly  in  that  part  of  the  mesial  surface  border- 
ing on  the  calcarine  fissure,  including-  the  cuneus  and  the  median 
occipitotemporal  or  lingual  gyrus.  The  strongest  opponent  to 
this  belief  has  been  Ferrier,  who  claimed  for  a  long  time  that  the 


*  Von  Monakow  states  that  lesions  located  strictly  in  the  motor  region  produce  only  degen- 
eration of  the  motor  tract,  but  when  the  parietal  convolutions  are  involved,  degeneration  of  the 
lemniscus  occurs.  The  fact  that  no  degeneration  occurs  in  the  sensory  tract  when  the  lesion 
is  confined  to  the  motor  area:  may  possibly  be  explained  by  the  theory  of  Mott,  above  referred  to. 


458 


CENTRAL  NERVOUS  SYSTEM. 


visual  centers  of  the  monkey  were  located  in  the  an^ailar  <j;yrus.'=' 
He  has  recently  modified  his  opinion  and  includes  with  this  area 
the  occipital  lobe,  which  toi^^ether  he  has  termed  the  occipito- 
angular  gyrus.  The  experiments  of  Monk.  Horsley,  Brown, 
and  Schiifer  have  conclusively  shown  in  animals  that  the  visual 
centers  are  located  in  the  occipital  lobes.  1  lorsley  and  Schiifer 
found  that  extensive  destruction  of  the  occipital  with  a  small 
part  of  the  temporal  lobes  of  a  monkey's  brain  was  followed  by 
bilateral  homonymous  hemianopsia.  Brown  and  Schafer  de- 
stroyed both  angular  gyri  in  a  monkey  without  the  occurrence 
of  any  loss  of  vision,  which  disproves  the  claim  of  Ferrier.      M, 


Fig.  226. — CoKTicAL  Visual  Centers 
ON  THE  Outer  Surface  of  the  Hemi- 
sphere. The  darker  shading  indicates 
the  region  of  the  half-vision  center  (the 
precise  limitation  of  which  is  not  yet 
known)  ;  the  lighter  shading  is  that  of 
the  supposed  higher  visual  center. — 
{A/Ur  Goivers.) 


Fig.  227.  —  Inner  Aspect  of  the 
Rkjht  Hemisphere.  Probable  posi- 
tion of  the  visual  center  in  the  occipital 
lobe  and  of  the  olfactory  center  in  the 
uncinate  gyrus  (U). — {After  Go-wers.) 


Allen  Starr  proves  this  fact  in  man  by  the  collection  ol  twenty- 
four  cases  of  lesions  of  the  angular  gyrus  without  the  slightest 
disturbance  of  vision.  A  number  of  clinical  cases  are  on  record 
which  prove  that  the  visual  centers  in  man  are  located  in  the 
occipital  lobes.  Starr  was  able  in  1884,  from  a  collection  of 
twenty-seven  cases  of  lesions  of  the  occipital  lobe,  to  definitely 
locate  the  visual  area  in  that  lobe.  Seguin,  in  1886,  reported 
forty  cases  from  literature,  all  of  which  are  confirmatory  of  the 
same  fact. 

The  cases  of  Seguin,  Hun,  Monakow,  Dejerine,  and  Henschen 


*  Ferrier  still   maintains  that  the  macular  fields  or  areas  of  central  vision  are  in  the  angular 


gyn. 


,-<(i^Jl^^^ 


T?^'^}?/:  Optic  tract 


.Grrpora  OiUcu^ngejn/- 


Fig.  228.— Diagram  of   Course  of   Optic  Nerve-fibers,  from  the  Cortex  to  the 
Retina. — {After  Sahli,  Modified  and  Extended,  from  Tyson.) 

459 


CEREBRAL  LOCALIZATION.  461 

all  show  that  lesions  of  that  part  of  the  mesial  surface  of  the 
occipital  and  adjacent  part  of  the  temporal  lobe  bordering  on 
the  calcarine  fissure  are  invariably  attended  by  partial  or  com- 
plete bilateral  homonymous  hemianopsia — that  is,  a  paralysis  of 
the  fields  of  vision  opposite  to  the  lesion.  Hence,  this  area 
may  be  termed  the  half-vision  center.  The  visual  area  may  be 
affected  by  irritative  or  destructive  lesions.  In  the  former  case 
the  patient  suffers  from  periodic  nervous  discharges,  resulting  in 
visual  hallucinations,  such  as  a  sudden  flash  of  light,  frequently 
followed  by  temporary  blindness  in  the  opposite  halves  of  the 
visual  fields.  Destruction  of  this  area  on  one  side  produces  the 
characteristic  visual  loss  known  as  bilateral  homonymous  hemi- 
anopsia, while  destruction  of  the  visual  areas  of  both  sides  pro- 
duces total  blindness.  It  will  thus  be  seen  that  hallucinations 
of  vision  and  bilateral  homonymous  hemianopsia  are  as  charac- 
teristic for  irritative  or  destructive  lesions  of  the  visual  area  as 
are  partial  unilateral  convulsions  and  motor  paralysis  for  lesions 
of  the  motor  region.  In  order  to  understand  the  peculiar  form 
of  visual  defect  known  as  homonymous  hemianopsia,  it  will  be 
necessary  to  recall  to  mind  the  course  of  the  optic  tract.  The 
fibers  of  this  tract,  which  have  their  origin  from  the  cells  of  the 
temporal  half  of  each  retina,  do  not  decussate  in  the  optic 
chiasm,  but  pass  backward  on  the  same  side  ;  while  those  that 
proceed  from  the  cells  of  the  nasal  half  of  each  retina  cross 
over  in  the  chiasm  to  join  'the  fibers  from  the  temporal  half  of 
the  opposite  retina,  thus  forming  the  optic  tract  of  that  side. 
The  fibers  then  continue  backward  to  terminate  about  the  cells 
of  the  external  geniculate  body,  the  pulvinar  of  the  optic  thala- 
mus, and  the  anterior  corpus  quadrigeminum.  From  the  cells 
of  these  primary  optic  centers  new  fibers  start  out,  which  pass 
through  the  extreme  end  of  the  posterior  division  of  the  internal 
capsule  and  thence  radiate  through  the  centrum  semiovale,  to 
terminate  about  the  cortical  cells  of  the  occipital  lobe,  chiefly 
the  cuneus  and  lingual  gyrus  ;  thus,  for  example,  the  right  oc- 
cipital lobe  has,  terminating  about  its  cortical  cells,  the  fibers  from 
the  temporal  half  of  the  right  retina  and  those  from  the  nasal 
half  of  the  left  retina.  It  may  be  stated  that  the  temporal 
halves  of  the   retinae  receive  impulse  from  the  nasal  halves  of 


402  CENTRAL   XERVDL'S   SYSTEM. 

the  visual  fields,  ami  the  nasal  halves  of  the  retinae  receive  im- 
pulses from  the  temporal  halves  of  the  visual  fields.  Therefore, 
a  lesion  involving-  the  right  visual  area  in  the  occipital  lobe  will 
cause,  owing-  to  the  fact  that  the  right  optic  tract  contains  the 
fibers  from  the  temporal  half  of  the  right  and  the  nasal  half  of 
the  left  retina,  a  paralysis  of  the  left  halves  of  the  visual  field, 
because  of  a  loss  of  function  of  the  right  halves  of  each  retina. 
This  defect  is  called  bilateral  homonymous  hemianopsia. 


RETINAL  REPRESKNTAriOX   IN    I'HE  OCCIPITAL  CORTEX. 

The  very  interesting  case  reported  by  Henry  Hun,  in  connec- 
tion with  others  collated  by  Seguin  and  Henschen,  seem  to 
prove  that  the  different  quadrants  of  the  retinae  are  represented 
by  different  areas  of  the  median  surface  of  the  occipital  cortex. 
In  Hun's  case  there  w^as  a  defect  in  the  lower  left  quadrant 
of  each  field  of  vision,  with  a  corresponding  atrophy  of  the 
lower  half  of  the  right  cuneus.  Henschen  locates  the  cortical 
center  for  the  lower  quadrant  of  each  retina  in  the  superior 
part  of  the  lingual  gyrus. 


COLOR  VISION. 

In  regard  to  a  cortical  center  for  the  representation  of  co|or 
vision,  nothing  positive  is  known.  Gowers  believes  it  may  be 
located  in  the  anterior  division  of  the  occipital  lobe,  while  Hen- 
schen places  it  in  the  vicinity  of  the  calcarlne  fissure. 


THE   AUDITORY   CENTERS. 

Apart  from  the  results  of  the  experiments  of  Schafer  and 
Brown,  physiologists  and  clinicians  agree  in  locating  the  centers 
for  audition  in  the  temporal  lobes.  The  above-mentioned  physi- 
ologists experimented  by  destroying,  on  each  side,  the  superior 
temporal  lobes  of  six  monkeys,  and  in  one  animal  the  entire 
temporal  lobe  was  removed  without  producing  the  slightest  loss 
of  hearing,  even  of  a  temporary  character.      The  experiments 


CEREBRAL  LOCALIZATION.  463 

of  Ferrier,  both  those  before  and  those  undertaken  since  the 
pubHcation  of  the  results  of  the  work  of  Schafer  and  Brown,  do 
not  bear  out  the  conclusions  of  these  latter  observers.  Ferrier 
locates  the  auditory  centers  in  the  posterior  part  of  the  superior 
or  first  temporosphenoid  convolution  on  each  side.  Electric 
excitation  of  this  area  on  either  side  invariably  produced  in  the 
monkey  retraction  or  picking  up  of  the  opposite  ear,  associated 
with  the  opening  of  the  eyes  and  dilatation  of  the  pupils,  with 
turning  of  the  head  and  eyes  to  the  opposite  side.  He  further 
states  that  he  placed  a  monkey  on  a  table,  and  while  all  was 
still  he  made  a  shrill  whistle  close  to  the  animal's  right  ear  ;  im- 
mediately the  ear  was  retracted  and  the  animal  turned  with  a 
look  of  intense  surprise,  with  eyes  widely  opened  and  pupils 
dilated,  toward  the  side  from  which  the  sound  proceeded,  thus 
proving  that  the  stimulus  of  an  external  sound  to  a  normal  ani- 
mal produced  exactly  the  same  phenomena  as  resulted  from 
electric  stimulation  of  the  auditory  center.  The  similar  result 
in  both  cases  is  due  to  reflex  action,  in  the  former  case  to  a 
stimulus  (electiic)  applied  directly  to  the  auditory  center,  and 
in  the  latter  case  is  due  to  stimuli  carried  to  the  same  center  by 
way  of  the  auditory  tract.  These  experiments,  with  others,  on 
animals  whose  sense  of  hearing  is  very  acute  has  led  Ferrier  to 
state  that  irritation  of  the  superior  temporosphenoid  convolu- 
tion of  one  side  excites  subjective  auditory  sensations  of  the 
ear  of  the  opposite  side,  such  as  pricking  of  the  ear  and  turning 
of  the  head  and  eyes  toward  the  side.  The  destruction  of  this 
area  on  either  side  caused  an  absence  of  the  usual  reaction  to 
the  auditory  stimuli  coming  from  the  ear  opposite  to  the  lesion 
after  the  ear  on  the  side  operated  on  was  carefully  plugged. 
Destruction  of  both  superior  temporal  gyri  caused  complete 
absence  ,of  the  response  to  auditory  stimuli,  which  invariably 
attracted  the  attention  of  a  normal  animal.  This,  seems  con- 
clusive proof  that  in  the  monkey  there  are  two  centers  of  hear- 
ing, one  in  each  superior  temporal  gyrus,  the  destruction  of  one 
producing  deafness  in  the  opposite  ear,  and  the  destruction  oi 
both  producing  total  deafness. 

In  man  the  centers  of  audition  are  located  in  the  same  parts 
of  the  temporal  lobes  as  Ferrier  has  located  them  in  the  mon- 


464  CENTRAL   NERVOUS  SYSTEM. 

key.  This  has  been  proven  by  a  few  well-recorded  cases  with 
autopsies.  These  cases  show  that  lesions  of  the  superior  tem- 
poral oyri  give  rise  to  two  sets  of  symptoms — /.  c,  those  due 
to  irritation  and  those  due  to  loss  of  function.  The  former  are 
simple  discharges  of  energy  from  these  centers,  resulting  in 
subjective  auditory  sensations  which  are  referred  to  the  ear 
opposite  to  the  lesion  ;  the  latter  cause  partial  or  complete 
deafness.  The  irritative  symptoms  are  often  merely  the  pre- 
monitory symptoms  or  aurce,  which  precede  the  more  general 
symptoms  of  the  lesion.  Such  a  mode  of  onset  occurred  in 
two  cases  reported  by  Gowers.  In  the  first  case  the  convul- 
sions (general  symptom)  were  ahvays  preceded  by  an  auditory 
aura  referred  to  the  opposite  ear.  At  the  autopsy  a  tumor  was 
found  beginning  in  the  superior  temporal  gyrus.  In  the  second 
case  the  unilateral  convulsions  were  preceded  by  an  aura  of 
loud  noise,  as  of  machinery.  In  this  case  a  tumor  was  found 
involving  the  middle  of  the  superior  temporal  gyrus.  The 
cases  of  Shaw,  Wernicke,  Friedlander,  and  Mills  prove  conclu- 
sively that  destruction  of  both  superior  temporal  gyri  in  man 
produces  total  deafness.  The  combined  results  of  physiologic 
experiments  and  pathologic  observation  leave  no  room  for 
doubt  that  the  centers  of  hearing  are  located  in  the  superior 
temporal  gyrus  of  each  side.  It  seems  probable  that  in  man 
the  sense  of  hearing  of  each  ear  is  bilaterally  represented,  be- 
cause of  the  fact  that  a  lesion  of  the  superior  temporal  gyrus 
of  one  side  produces  only  partial  deafness  of  the  opposite  ear, 
which  deafness  frequently  passes  away,  whereas  bilateral  lesions 
occasion  complete  and  permanent  deafness.  Against  this  theory 
of  bilateral  representation,  and  in  support  of  the  theory  of  a 
single  center  for  the  reception  of  auditory  stimuli  from  the 
opposite  ear,  is  the  very  important  and  well-known  case  of  Ber- 
tillon,  the  statistician,  who  suffered  from  complete  loss  of  hear- 
ing on  the  left  side  since  childhood.  At  death  the  left  superior 
temporal  gyrus  was  found  to  be  very  much  larger  than  that 
of  the  rigrht  side. 


'  CEREBRAL  LOCALIZATION.  465 

THE  CENTERS  FOR  LANGUAGE. 

Clinicopathologlc  investigations  have  positively  shown  that 
there  are  at  least  five  distinctive  cortical  areas  governing  the 
various  processes  which  are  concerned  in  spoken,  written,  or 
sign  language.  These  centers,  in  general,  may  be  divided  into 
two  types, — sensory  and  motor, — and  are  as  follows  :  First,  a 
center  for  the  reception  of  the  memories  of  spoken  words ; 
second,  a  center  for  the  reception  of  the  memories  of  the  appear- 
ance of  objects  as  seen  and  of  words  as  written  ;  third,  a  center 
for  the  reception  of  the  appearance  of  objects  gained  through 
the  sense  of  touch  ;  fourth,  a  center  for  the  memory  of  the 
muscular  movements  necessary  for  the  performance  of  articu- 
late speech  ;  fifth,  a  center  for  the  memory  of  muscular  move- 
ments concerned  in  writing.  It  may  be  mentioned,  before 
describing  the  location  of  these  various  centers,  that  in  the  great 
majority  of  individuals  who  are  right-handed  from  birth  these 
centers  are  active  only  in  the  left  cerebral  hemisphere,  and  that  in 
the  left-handed  they  are  active  in  the  right  hemisphere  only.  A 
possible  explanation  for  this  fact  may  be  that  of  heredity  and 
education.  Bastian  states,  as  to  the  causes  which  have  deter- 
mined the  greater  or  almost  exclusive  influence  of  the  left  hemi- 
sphere in  inciting  speech  movements,  and,  therefore,  in  acting 
upon  the  bulbar  motor  centers,  only  conjectures  can  be  offered. 
It  is,  however,  now  pretty  generally  agreed  that  the  immediate 
or  proximate  cause  is  to  be  found  in  the  fact  of  the  predominant 
use  of  the  right  hand,  which  entails  a  greater  functional  activity 
of  the  left  hemisphere.  This  view  rests  principally  upon  the  now 
ascertained  fact  that,  in  the  great  majority  of  cases  in  which 
aphasia  has  occurred  as  a  result  of  brain-lesions  in  the  right 
hemisphere,  those  so  affected  have  been  left-handed. 

It  is  a  well-known  fact  that  in  right-handed  persons  there  is  a 
greater  convolutional  development  of  the  lower  part  of  the  left 
frontal  lobe  than  the  right.  On  examination  of  the  brains  of 
two  left-handed  persons,  Bramwell  found  the  opposite  condition 
— that  is,  a  greater  development  and  complexity  of  the  convo- 
lutions in  the  right  frontal  lobe. 

It  may  also  be  stated  that,  in  case  of  the  destruction  of  any 


466  CENTRAL  NERVOUS  SYSTEM. 

one  of  these  centers  concerned  in  speech,  the  centers  in  the 
opposite  hemisphere  which  have  been  inactive  or  latent  oradiially 
take  on  the  function  of  the  center  which  has  been  destroyed. 
The  defect  in  speech  is  thus  compensated  for,  this  occurring"  the 
sooner  the  vounoer  the  individual  affected. 


THE  CENTER  FOR  THE  RECEPTION  OF  HEARD  WORDS. 

The  experiments  of  Monk  on  the  lower  animals  have  posi- 
tively located  this  center  in  the  temporal  lobes.  This  ob- 
server found,  if  he  extirpated  corresponding'  areas  of  tlie  tem- 
poral lobes  of  each  hemisphere  of  the  dog's  brain,  that  the 
animal,  after  sufficient  time  had  elapsed  for  recovery  from  the 
shock  of  the  operation,  could  recognize  sounds  as  usual,  and 
would  give  evidence  of  such  recognition  by  the  usual  signs,  such 
as  pricking  up  of  the  ears,  partial  rotation  of  the  head,  etc.,  but 
these  sounds  conveyed  no  meaning  ;  in  other  words,  the  animal 
did  not  understand  what  he  heard.  The  familiar  commands  of 
his  master,  although  heard,  were  not  heeded,  because  the  animal 
failed  to  recoirnize  the  meaninor.  To  this  condition  Monk  crave 
the  name  of  mind-deafness.  In  man,  the  center  for  the  recep- 
tion of  the  memories  of  heard  words  is  in  the  posterior  half  of 
the  superior  and  middle  temporal  convolutions  of  the  left  side 
in  right-handed  persons,  and  in  the  same  location  in  the  right 
temporal  lobe  for  left-handed  persons.  This  statement  is  based 
upon  data  obtained  from  the  study  of  the  position  of  the  lesion 
in  a  number  of  carefully  recorded  cases  of  sensory  aphasia 
where  the  visual  and  motor  speech-centers  were  found  in  a 
normal  condition.  Such  cases  have  been  recorded  by  Wernicke, 
Kussmaul,  Seppilli,  Hitzig,  and  Mills.  Seppilli  has  collected 
seventeen  cases,  in  all  of  which  the  lesion  was  located  in  the 
same  area.  Destructive  lesions  in  this  area  of  the  temporal 
lobe  produce  the  characteristic  defect  of  speech  known  as  audi- 
tory aphasia  (Bastian),  or  mind-deafness  (Kussmaul),  as  it  is 
more  commonly  termed.  In  persons  suffering  from  this  affec- 
tion, although  the  sounds  of  the  words  are  heard  as  usual,  the 
person  is  unable  to  understand  what  is  said  because  the  mental 
image  of  the  object  stored  in  that  center  and  recalled  by  the 


CEREBRAL  LOCALIZATION. 


467 


word  has  been  destroyed.  Broadbent,  Kussmaul,  and  Charcot 
agree  that  a  center  for  ideas  exists  and  that  its  most  probable 
location  is  in  the  lower  posterior  part  of  the  outer  surface  of 
the  temporal  lobe.     This  center  is  in  communication  with  all 


Wernicke. 


Girandeau. 


Eichhorst.  Hitzig. 

Fig.  229. — Situation  of  Lesions  Causing  Word-deafness  Only. — {F>-om  Starr.) 


the  receptive  centers  of  the  cortex  by  means  of  the  association 
tracts.  Thus,  while  the  individual  perceptions  of  an  object  are 
conducted  to  the  various  receptive  centers  of  the  cortex,  the 
mental  image,  concept,  or  idea  of  the  object,  which  is  the  result 
of  the  association  of  its  various  perceptions,  is  stored  up  in  this 


46S  CENTRAL  NERVOUS  SYSTEM. 

so-called  center  for  ideas,  each  idea  being-  symbolized  by  a  name 
which  is  used  in  giving  expression  to  it  in  speech.  Disease  of 
this  center  produces  partial  or  complete  inability  on  the  part 
of  the  person  afl'ected  to  recall  to  mind  the  sounds  of  the 
words,  and  hence  the  words  can  not  be  spoken  although  they 
may  be  repeated  after  another.  This  form  of  speech-defect  is 
called  verbal  or  amnesic  aphasia  ;  the  loss  involves,  particularly, 
proper  names  and  substantives.  In  a  case  now  under  my  ob- 
servation the  only  defect  is  the  loss  of  memory  of  proper  names, 
the  patient  being  unable  to  introduce  to  others  his  most  intimate 
friends,  because  he  can  not  recall  to  mind  their  names.  Such 
patients,  when  they  can  not  recall  the  proper  names,  frequently 
resort  to  a  paraphrase  so  that  they  may  convey  the  idea.  Such 
was  the  case  in  a  patient  of  Kussmaul,  where  there  was  a  loss 
in  the  memory  of  nouns,  but  that  of  verbs  was  retained.  A  pair 
of  scissors  he  called  "that  which  one  cuts  with"  ;  a  window, 
"that  through  which  one  sees  and  through  which  light  comes." 
In  support  of  the  existence  of  a  center  for  ideas.  Mills  has  re- 
corded a  very  interesting  case  of  verbal  amnesia,  with  partial 
word-blindness  but  not  letter-blindness,  and  with  left  lateral 
homonymous  hemianopsia.  At  the  autopsy  a  granular,  tumor- 
like mass,  about  the  size  of  a  hickory-nut,  was  removed  from 
the  surface  of  the  posterior  fourth  of  the  third  temporal  gyrus, 
and  the  posterior  half  of  the  third  and  a  small  part  of  the  fourth 
temporal  gyri  were  likewise  involved.  On  section  of  the  tem- 
poral lobe  a  tumor  was  disclosed,  having  its  oldest  part  about 
the  middle  of  the  third  temporal  and  passing  slightly  into  the 
second  temporal.  In  addition,  a  softened  area,  extending  into 
the  middle  of  the  occipital  lobe,  was  discovered.  From  the 
result  of  this  case.  Mills,  who  prefers  to  call  this  center  the 
"  naming  center,"  locates  it  in  the  posterior  part  of  the  third  and 
fourth  temporal  gyri.  It  may  be  true  that  in  this  location  a 
separate  center  exists  destruction  of  which  produces  verbal 
amnesia,  but  it  is  also  true  that  this  latter  condition  is  also  asso- 
ciated with  partial  word-deafness,  and  as  a  residual  condition  in 
cases  of  motor  aphasia,  the  lesions  in  both  of  which  cases  are 
distinctlv  localizable. 


CEREBRAL  LOCALIZATION. 


469 


THE    CENTER    FOR   THE    RECEPTION  OF  MEMORIES  OF    THE 
APPEARANCE    OF    OBJECTS    SEEN   AND  FOR  THE  APPEAR- 
ANCE OF   WORDS  AS  WRITTEN  OR  PRINTED. 
The  former  center — /.  e.,  the  center  for  the  memories  of  seen 

objects— is  located,  according  to   Freund,  in  the  right  angular 


Broadbent. 


Henschen. 


Hun.  Macewen. 

Fig.  2:10.— Situation  of  Lesions  Causing  ^YoRD-BLIXDNEss  Only.— (/Vow  Siarr.') 


gyrus.  Destruction  of  this  area  produces  in  man  psychic  or 
mind-blindness — that  is,  a  condition  in  which  a  person  so  affected 
fails  to  recall  to  mind  the  visual  image  of  the  appearance  of  an 
object,  although  the  object  is  perfectly  seen.     This  condition  is 


470  CENTRAL  NERVOUS  SYSTEM. 

entirely  distinct  Irom  WDrel-blindness,  which  latter  condition  is,  in 
most  instances,  due  to  a  lesion  in  the  left  angular  gyrus.  It 
may.  however,  be  associated  with  the  former  condition,  when  a 
lesion  will  then  be  found  in  the  angular  gyrus  of  each  side. 
Freund  bases  the  foregoing  statement  upon  the  study  of  eight 
cases  with  autopsies,  five  from  literature  and  three  personal. 

The  center  for  the  reception  of  the  memories  of  the  appear- 
ance of  written  or  printed  language  is  located  in  the  angular 
gyrus  of  the  left  side  in  persons  who  are  right-handed,  and  in 
the  opposite  side  for  those  left-handed.  The  exact  location  of 
this  center  has  been  determined  by  the  study  of  lesions  found 
in  a  number  of  cases  of  pure  word-blindness,  all  of  which  were 
located  in  the  left  angular  gyrus,  and  were  unaccompanied  by 
visual  defects. 

Word-blindiicss,  oi"  alexia,  is  a  condition  in  which  written  or 
printed  words,  although  well  seen,  do  not  arouse  in  memory 
their  visual  images.  The  patient  that  is  word-blind  is  able  to 
recall  the  appearance  of  objects,  unless  he  has  at  the  same 
time  mind-blindness,  which  latter  condition  is  due,  in  most  in- 
stances, to  the  lesion  involving  the  angular  gyrus  of  the  right 
hemisphere.  In  complete  word-blindness  the  patient  is  unable 
to  w^rite  spontaneously,  because  the  memories  of  the  appear- 
ance of  words  are  lost,  and  he  is  unable  to  read  because  the 
words,  although  seen,  are  without  meaning.  If  this  condition 
is  incomplete,  he  may  be  able  to  recognize  and  name  individual 
letters  of  a  word  without  beinor  able  to  recognize  the  word  itself. 
Patients  in  this  condition  often  have  a  perfect  knowledge  of 
numerals  while  they  can  not  recognize  words  (Fig.  230). 


THE  CENTER   FOR  THE   RECEPTION  OF  THE  APPEARANCE  OF 
OBJECTS  GAINED  THROUGH  THE  SENSE  OF  TOUCH. 

Although  much  douljt  exists  at  the  present  time  as  to  the 
exact  location  of  a  center  for  the  appearance  of  an  object 
gained  through  the  sense  of  touch,  the  study  of  the  cases  of 
sensory  optic  and  tactile  aphasia,  recently  reported  by  Johannes 
Vorster,  prove  that  such  a  center  probably  exists  in  the  central 
convolutions   (sensorimotor  area)   and  is  connected  both   with 


CEREBRAL  LOCALIZATION.  471 

the  angular  gyrus  and  the  auditory  or  sensory  speech-center  in 
the  temporal  lobe  by  association  tracts  of  fibers.  Vorster  has 
collected  seven  cases  of  tactile  aphasia  from  literature  and  has 
added  one  personal  case,  in  all  of  which  sensory  optic  aphasia 
existed. 

In  order  to  have  tactile  aphasia,  both  bundles  of  association 
connecting  the  tactile  center  with  the  angular  gyrus  and  with 
the  auditory  sensory  speech-center  must  be  destroyed.  Hence 
tactile  aphasia  must  necessarily  be  accompanied  by  sensory 
optic  aphasia.  In  sensory  optic  aphasia  the  patient  is  unable  to 
name  an  object,  although  it  is  seen  and  recognized.  He  can 
recall  the  name  of  an  object  when  heard  and  can  name  the 
object  after  having  handled  it.  This  indicates  that  the  lesion 
has  destroyed  the  association  bundle  connecting  the  left  angu- 
lar -gyrus  with  the  auditory  receptive  speech-center  (inferior  or 
longitudinal  bundle)  ;  hence  the  sight  of  the  object  does  not 
recall  to  mind  its  name,  but  through  the  sense  of  touch  the 
tactile  center  is  brought  into  relation  with  the  auditory  center 
(superior  longitudinal  bundle),  and  therefore  the  patient  is  able 
to  name  the  object  after  having  handled  it. 

In  tactile  aphasia,  which  is  always  combined  with  optic  apha- 
sia, both  of  the  association  bundles  connecting  the  tactile  cen- 
ter with  the  angular  gyrus  (tactile  optic  acoustic  tract)  and 
auditory  center  and  the  tactile  acoustic  tract  connecting  the 
tactile  center  with  the  auditory  receptive  speech-center  are  de- 
stroyed. The  patient  is  not  only  unable  to  name  a  seen  object, 
but  is  also  unable  to  name  the  object  through  the  aid  of  his 
tactile  sense. 


THE  MOTOR  SPEECH-CENTER,  OR  CENTER  FOR  THE  RECEP- 
TION OF  THE  MUSCULAR  MEMORIES  NECESSARY  TO  PRO- 
DUCE SPEECH. 

To  Broca  is  due  the  credit  of  having  accurately  located  the 
motor  speech-center  in  the  posterior  part  of  the  inferior  left 
frontal  gyrus.  This  region  is,  therefore,  in  honor  of  the  dis- 
coverer, called  the  area  of  Broca.  This  location  he  determined 
from  the  study  of  seventeen  cases  of  aphasia  with  autopsies,  in 


472 


CENTRAL  NERVOUS  SYSTEM. 


sixteen  of  whicli  the  posterior  part  of  the  left  inferior  frontal 
gyrus  was  found  destroyed,  while  in  the  other  case  it  was  also 
affected,  but  in  addition  to  it  the  island  of  Reil  and  the  parietal 
lobe.  Since  Broca's  time,  hundreds  of  clinical  cases  with  autop- 
sies have  been  recorded,  which  have  verified  his  conclusions  as 
to  the  location  of  this  center.  In  this  area  are  stored  the  motor 
memories  necessary  to  give  expression  to  thought  through 
articulate  speech. 

When  Broca's  center  is  destroyed,  there  is  produced  the 
characteristic  speech-defect  known  as  motor  aphasia,  which  con- 
dition is  an  inability,  complete  or  partial,  on  the  part  of  the 
person  affected,  to  give  vocal  utterance  to  thought. 


Fig.  231. — Situations  of  Lesions  Cai"sing  Aphasia. — (^After  Starr,  from  Tyson.) 
I.   Lesion  of  word-deafness.     2.   Lesion  of  word-blindness.     3.   Lesion  of  motor  aphasia.     4. 

Supposed  lesion  of  agraphia. 


In  many  cases  of  complete  motor  aphasia  the  patients  may  be 
able  to  give  expression  to  a  few  very  familiar  words,  like  "yes  " 
or  "no,"  or  other  very  short  phrases.  These  "recurring  utter- 
ances," as  they  are  termed,  are  probably  the  result  of  the  excita- 
tion of  the  right  inferior  frontal  gyrus. 

There  is  an  actual  loss  of  the  power  of  speech  without,  in 
most  cases,  the  slightest  paralysis  of  the  muscles  concerned  in 
the  production  of  speech.  The  patient  can  not  repeat  words 
after  another,  nor  can  he  read  aloud.  In  many  cases  of  motor 
aphasia  there  is  also  an  inability  to  write — agraphia.  Agraphia 
was  so  often  found  associated  with  motor  aphasia  that  Trous- 
seau, Jackson,  and   Gairdner  were   led   to  believe  that  writing 


CEREBRAL  LOCALIZATION.  473 

was  performed  through  the  medium  of  Broca's  speech-center, 
and  that  a  separate  and  distinct  center  for  writing  did  not  exist. 
Several  cases  with  autopsies,  however,  have  been  recorded  to 
prove  that  motor  aphasia,  when  accompanied  with  agraphia,  is 
due  to  destruction  not  only  of  Broca's  speech-center,  but  also 
to  the  base  of  the  second  left  frontal  convolution — the  probable 
center  for  writing.  Such  cases  have  been  reported  by  Tambu- 
rini,  Marchi,  and  Simon. 

The  loss  of  the  faculty  of  writing  does  not  exist  in  every  case 
of  motor  aphasia  in  which  the  right  hand  is  not  paralyzed. 
Professor  Oppenheim,  of  Berlin,  has  reported  a  case  of  pure  motor 
aphasia  in  which  the  patient  was  able  to  say  only  the  words 
"yes"  and  "no,"  but  could  write  and  paint  during  the  whole 
period  of  his  illness.  Similar  cases  have  been  recorded  by 
Kahler,  W.  Ogle,  Guido  Banti,*  Wadham,  and  Byrom  Bramwell. 
At  the  autopsy  of  three  of  these  cases  the  lesion  was  strictly 
localized  to  Broca's  center. 


*A  right-handed  man,  aged  thirty-six,  who  was  able  to  read  and  write  correctly,  had  a 
sudden  apoplectic  attack  in  1877.  Recovering  consciousness  in  a  few  minutes,  he  was  found  to 
be  suffering  from  right  hemiplegia  and  loss  of  speech.  The  paralysis  of  the  limbs  disappeared 
almost  completely  during  the  following  night,  although  the  inability  to  speak  persisted. 

The  next  day  he  was  admitted  into  the  hospital,  and,  on  most  careful  examination,  his  con- 
dition was  found  by  Guido  Banti  to  be  as  follows:  "The  motility  of  the  limbs  of  the  right 
side  had  returned  to  their  normal  condition.  There  was  no  trace  of  paralysis  of  the  face  or 
tongue.  The  patient  made  ineffectual  attempts  to  speak  ;  he  could  not  articulate  a  single  word, 
not  even  isolated  syllables.  He  was  much  affected  by  this  mutism,  and  sought  to  make  himself 
understood  by  gestures.  I  asked  him  if  he  knew  how  to  write,  and  after  he  had  made  a  gesture 
in  the  affirmative  I  gave  him  what  was  necessary  and  told  him  to  write  his  name,  which  he  did 
immediately.  I  put  various  other  questions  to  him,  to  which  he  replied  similarly  by  writing.  I 
told  him  to  give  me  a  description  of  his  illness  and  he  wrote,  without  hesitation,  the  details 
above  reported.  I  showed  him  various  objects — pieces  of  money,  etc. — telling  him  to  write 
their  names,  and  he  did  so  without  making  any  mistakes.  Then,  instead  of  giving  him  these 
directions  by  word  of  mouth,  I  wrote  them  to  him,  in  order  to  thoroughly  convince  myself  that 
he  was  able  to  understand  writing.  He  replied  to  these  questions  with  perfect  correctness.  He 
always  wrote  very  rapidly,  and  did  not  seem  to  hesitate  to  choose  his  words.  He  made  no  mis- 
takes in  syntax  or  orthography.  He  could  understand  equally  well  ordinary  writing  and  print, 
and  when  one  spoke  to  him  he  grasped  at  once  the  meaning  of  the  questions,  and  never  wished 
to  have  them  repeated.  I  next  wrote  him  some  most  simple  words,  such  as  "  pain,"  "vim," 
etc.,  and  urged  him  ineffectually  to  read  them  aloud.  I  then  pronounced  myself  some  of  the 
words,  directing  him  to  repeat  them.  He  appeared  to  watch  with  great  attention  the  movement 
of  the  lips  whilst  I  spoke.  He  made  some  ineffectual  efforts  to  obey,  but  he  never  succeeded 
in  pronouncing  a  single  word." 

This  patient  died,  in  February,  1882,  from  an  aneurysm  of  the  aorta,  and  a  patch  of  yellow 
softening  was  found  situated  in  the  posterior  third  of  the  third  left  frontal  convolution,  and  ex- 
tending for  some  millimeters  only  in  the  white  substance. 


474  CENTRAL  NERVOUS  SYSTEM. 

The  fact  that  the  muscles  concerned  in  articulation,  owing  to 
a  lesion  which  causes  motor  aphasia,  are  not  paralyzed  is  prob- 
ably due,  in  most  cases,  to  the  fact  that  these  muscles  act  bilater- 
ally, anil  hence  are  bilaterally  represented  by  centers  of  action 
in  each  cerebral  hemisphere.  These  latter  centers  are  located 
in  the  extreme  posterior  part  of  the  third  frontal  and  the  lowest 
l)art  of  the  ascending  frontal  and  parietal  gyri  of  each  side.  In 
order,  therefore,  to  have  a  complete  paralysis  of  the  muscles  of 
articulation,  both  centers  must  be  destroyed.  A  few  such  cases 
are  on  record,  one  of  the  most  typical  of  which  has  been  de- 
scribed by  Barlow.'" 

The  motor  speech-area  then  really  consists  of  two  parts  : 
first,  the  true  center  for  the  storing  of  muscular  memories  of 
words  for  speech,  and,  secondly,  the  motor  centers  controlling 
the  muscles  necessary  to  pronounce  the  words.  A  lesion  of  the 
former  causes  true  motor  aphasia,  while  a  lesion  of  the  latter 
usually  causes  only  a  temporary  paralysis  of  the  muscles  of 
articulation.t 

Frequently,  in  people  of  limited  education,  who  read  little, 
and  then  only  aloud  or  by  moving  the  lip-muscles,  the  occur- 
rence of  motor  aphasia  is  usually  complicated  by  word-blind- 
ness, or  alexia. 

*  See  "British  Medical  Journal,"  July  28,  1877. 

fThe  following  case  reported  by  Oder  and  copied  from  the  book  of  Joseph  Collin,  on  the 
"  Faculty  of  Speech,"  shows  that  the  exact  location  of  the  cortical  center  for  the  articulatory 
muscles  is  in  the  inferior  pnrt  of  the  ascending  frontal  and  parietal  gyri.  It  also  shows  that 
this  center  is  entirely  distinct  from  the  motor  speech-center,  and  when  destroyed  on  the  left 
side,  produces  a  condition  of  dysarthria  identical  with  pseudobulbar  paralysis. 

A  man  sixty  years  old,  who  had  previously  been  well,  suddenly  developed  difficulty  in 
speaking  ;  speech  became  indistinct  and  blurred,  and  saliva  trickled  from  the  mouth.  On  ad- 
mission into  the  hospital  it  was  found  that  there  was  paresis  of  the  right  side  of  the  face,  more 
marked  in  the  lower  part  and  at  the  angle  of  the  mouth,  and  not  involving  the  orbicularis  pal- 
pebrarum. He  was  perfectly  conscious  and  understood  all  that  was  said  to  him,  had  no  hemi- 
plegia, and  his  only  trouble  was  incapacity  to  enunciate  words,  due  to  difficulty  in  moving  the 
tongue,  lips,  and  other  muscles  of  articulation.  There  was  no  aphasia,  and  the  voice  was  nor- 
mal. There  was  difficulty  in  swallowing  liquids.  He  died  five  days  after  the  onset  of  pneu- 
monia. On  examining  the  brain  there  was  found,  in  the  lower  part  of  the  left  ascending  fron- 
tal gyrus,  just  above  the  Sylvian  fissure,  a  blood-clot  which  had  pushed  its  way  through  the  cor- 
tex, and  had  destroyed  almost  entirely  the  cortical  substance  of  the  lower  end  of  the  central 
convolutions.     The  foot  of  the  third  frontal  convolution  was  normal. 


CEREBRAL  LOCALIZATION. 


475 


THE  CORTICAL  CENTERS  FOR  WRITING. 

Much  doubt  exists  as  to  the  exact  location  of  the  cortical 
area  concerned  in  writing.  Some  authors  believe,  owing  to  the 
fact  that  motor  aphasia  and  agraphia  are  so  often  combined,  that 
no  separate  center  exists  for  writing,  this  center  being  identical 
with  that  for  speech.   Bastian  has  shown,  however,  by  the  records 


Fig.  232. — Diagram  Showing  Location  of  Tumor  which  Produced  Complete 
Agraphia  (Author's  Case). 


of  several  cases  with  autopsies,  that  when  agraphia  coexists 
with  motor  aphasia,  it  is  usual  to  find  the  lesion  involving  the 
base  of  the  second  left  frontal  gyrus,  together  with  Broca's 
center.  ,  In  order  to  determine  whether  a  separate  center  exists 
for  the  reception  of  the  muscular  memories  concerned  in  writ- 
ing, a  case  must  be  found  in  which  a  lesion  of  a  certain  locality 
must  produce  agraphia  without  motor  aphasia,  paralysis  of  the 
hand,  or  word-  or  mind-blindness. 

The  only  case  with  autopsy  which  fulfils  the  before-men- 
tioned requirements  is  the  author's  case  of  a  glioma  at  the 
base  of  the  second  left  frontal   convolution,  in  which  the  only 


476  CKXTRAL  NHRVOUS  SVSTKM. 

localizing-  symptom  was   agraphia   unconibincd   with  any   lorm 
of  aphasia.'-' 


♦Author's  Case  ok  Agraphia.! — The  patient,  an  intelligent  Irish  woman,  received  her 
education  in  the  public  schools.  Her  age  is  thirty-seven,  and  .she  has  i)een  married  for  fifteen 
years ;  has  always  enjoyed  excellent  health  up  to  the  onset  of  the  present  illness,  which  began 
about  Christmas-time,  1897.  At  that  time  she  began  to  fail  in  strength  and  had  several  attacks 
of  vertigo  without  falling,  and  unattended  with  nausea  or  vomiting.  A  short  time  afterward  she 
developed  severe  frontal  and  occipital  headaches,  with  occasional  attacks  of  vomiting.  The 
headaches  continued  with  increasing  sevatity  until  the  fatal  issue.  In  March,  1898,  she  noticed 
that  her  sight  was  failing  and  that  she  could  not  read  coarse  print  without  the  use  of  her  glasses. 
At  about  the  same  time  she  began  to  complain  of  a  numbness  in  the  right  arm.  At  no  lime 
during  her  illness  did  she  have  a  unilateral  or  general  convulsion.  Her  bowels  have  been  rather 
constipated  ;  has  had  perfect  control  over  her  bladder.  Has  menstruated  regularly  and  in  a 
normal  manner.  Patient  converses  intelligently,  makes  no  errors,  and  her  memory  for  past  and 
recent  events  is  good.  At  no  time  during  her  illness  has  she  had  the  slightest  difficulty  in  giving 
expression  to  her  thoughts  by  articulate  speech.  Physical  examination  of  chest  elicited  no 
morbid  changes;  throat  normal,  temperature  normal,  pulse  68.  Examination,  April  5,  1898. 
Patient  five  feet  four  inches  in  height ;  weight,  140  pounds.  Head  well  formed  and  symmet- 
ric; no  evidence  of  previous  injury;  no  exostosis;  percussion  of  scalp  elicits  no  tenderness. 
Veins  of  forehead  not  prominent ;  pupils  moderately  and  equally  dilated,  respond  actively  to 
light  and  accommodation.  Wernicke's  hemiopic  pupillary  phenomenon  present.  No  hemian- 
opsia. Marked  optic  neuritis  of  both  eyes.  Owing  to  paresis  of  the  right  external  rectus 
muscle,  the  right  eyeball  could  not  be  rotated  outward,  but  its  movements  upward,  downward, 
and  inward  were  found  normal  ;  diplopia  existed ;  excursion  of  left  eyeball  normal ;  color- 
vision  noimal.  Drum-membranes  appeared  normal ;  hearing  distance  for  watch  in  each  ear  was 
three  feet.  Movements  of  tongue  normal  ;  no  fibrillation  or  atrophy.  Senses  of  taste  and  smell 
normal.  Soft  palate  and  uvula  move  in  a  normal  manner.  No  loss  of  sensation  over  buccal  or 
pharyngeal  mucous  membranes.  Movements  of  vocal  cords  perfect ;  no  difficulty  in  swallow- 
ing. No  stiffness  of  neck-muscles  or  those  of  spine.  Both  sides  of  face  symmetrically  formed; 
no  evidence  of  facial  paralysis.  Patient  is  able  to  perform  in  a  normal  manner  symmetric  bi- 
lateral movements.  Grip  of  right  hand  is  slightly  weaker  than  that  of  left.  Dynamometer, 
inner  scale,  right,  50;  left,  75.  No  muscular  atrophy  anywhere  discoverable.  Both  fine  and 
coarse  movements  of  the  right  and  left  hands  and  arms  normal.  Movements  of  lower  extremi- 
ties normal.  The  strength  of  both  sides  alike.  Careful  examination  of  the  skin  of  the  entire 
body  showed  no  sensory  disturbances.  No  edema  or  other  vasomotor  changes.  The  most 
careful  reinforcement  failed  to  elicit  the  presence  of  patella  tendon  reflexes.  No  ankle-clonus ; 
superficial  reflexes  present  not  exaggerated.  No  ataxia  in  upper  or  lower  extremities.  The 
sense  of  posture  normal.     .She  has  always  been  right-handed.      Romberg's  symptom  absent. 

Speech. — Patient  recognizes  and  names  correctly  any  object  placed  before  her.  She  can 
recognize  and  accurately  name,  with  her  eyes  closed,  any  familiar  object  when  placed  in  her 
right  hand,  such  as  coins  and  the  like.  She  understands  perfectly  what  is  said  to  her.  She 
recognizes  familiar  hymns.  She  can  repeat  words  after  another,  and  speaks  voluntarily  without 
the  slightest  hesitation,  and  always  correctly.  She  can  read  correctly,  with  the  aid  of  glasses, 
ordinary-sized  print  or  writing.  She  recognizes  numerals  at  once.  The  only  difficulty  present 
is  a  total  inability  to  write.  Although  she  understands  perfectly  written  language  and  can  read 
to  herself  or  aloud,  she  can  not  write  voluntarily  nor  form  correctly  a  single  letter,  and  cannot 
write  from  dictation  or  copy.  She  holds  the  pen  in  a  perfect  manner  and  executes  movements 
with  it  as  if  to  write  ;  her  writing  consisting,  however,  of  nothing  more  than  a  series  of  united 

•f"  "  The  American  Journal  of  the  Medical  Sciences,"  May,  1899. 


CEREBRAL  LOCALIZATION.  477 

Charcot  and  Dutil  and,  recently,  Eskeridge  have  each  re- 
ported a  case  which  nearly  fulfils  the  foregoing  requirements. 
In  the  case  of  Charcot  and  Dutil  a  woman,  after  an  apoplectic 
attack,  had  no  symptom  save  that  of  pure  motor  agraphia. 
Some  years  later  a  similar  attack  produced  motor  aphasia,  and, 
still  later,  recurring  attacks  resulted  in  the  condition  of  speech- 
lessness known  as  pseudobulbar  paralysis.  At  the  autopsy 
there  was  found  a  focus  of  softening  in  the  foot  of  the  second 
left  frontal  gyrus,  one  in  "the  foot  of  the  third  left  frontal,  and 
three  foci  in  the  right  hemisphere.  It  seems  probable,  owing 
to  the  long  duration  of  the  agraphia  without  aphasia,  that  the 
lesion  causing  the  former  was  the  focus  of  softening  located  at 
the  foot  of  the  second  left  frontal  convolution,  and  the  motor 


curves.  She  was  unable  to  write  with  her  left  hand,  as  she  was  not  ambidextrous.  The  fine  and 
coarse  muscular  movements  of  the  right  hand  are  executed  in  a  perfect  manner,  and  there  exists 
no  paralysis  of  the  muscles  of  the  hand,  forearm,  or  arm.  Before  the  present  illness  began  she 
could  write  perfectly.  She  showed  me  some  of  her  writing,  which  was  excellent.  This  con- 
dition of  complete  agraphia  continued  throughout  her  illness,  and  was,  with  the  exception  of 
the  gradual  development  of  a  slow  cerebration,  the  only  localizing  symptom  present.  At  no  sub- 
sequent time  was  there  found  the  slightest  evidence  of  motor  or  any  form  of  sensory  aphasia. 
She  never  became  paralyzed  or  developed  any  sensory  symptoms,  and  hemianopsia  or  alexia  were 
never  present.     She  was  operated  upon  July  19,  1898,  and  died  July  21,  1898. 

Autopsy,  July  22,  1898,  10.30  A.  M.  The  head  only  permitted  to  be' examined.  Opening 
in  skull,  4.5  by  4.75  cm.  Elevation  of  hernia  cerebri  above  dura  was  2  cm.  Dura  everywhere 
free  ;  vessels  of  pia  injected.  Left  cerebral  hemisphere  markedly  hemorrhagic.  Softening  of 
the  hernia  cerebri  and  surrounding  brain-tissue  ;  pia  not  adherent,  save  at  location  of  new  growth 
which  was  found  occupying  the  foot  of  the  second  frontal  convolution,  being  distinctly  separated 
from  the  arm-area  by  the  precentral  sulcus,  which  sulcus  was  in  this  case  well  developed.  The 
growth  was  elevated  about  ^  of  a  centimeter  above  the  surrounding  cortex,  was  slightly 
irregular  in  outline,  of  a  distinctly  firm  consistency,  and  oval  in  appearance.  Its  longest 
diameter  was  2^  cm.  The  pia  was  intimately  adherent  to  it.  On  section,  the  tumor  was  seen 
to  extend  downward  and  inward  as  far  as  the  roof  of  the  anterior  cornu  of  the  lateral  ventricle 
and  forward  to  near  the  apex  of  the  frontal  lobe.  The  left  third  or  inferior  frontal  convolution, 
throughout  its  whole  extent,  was  found  macroscopically  perfectly  normal,  as  was  its  associated 
centrum  ovale.  The  centrum  ovale  of  the  superior  or  first  frontal  convolution  was,  toward  its 
ventral  part,  infiltrated  by  the  growth.  The  motor  convolutions,  in  their  middle  third,  formed  a 
part  of  the  hernia  cerebri.  This  area  was  filled  with  multiple  capillary  hemorrhages,  the  result 
of  the  sudden  relief  of  the  intracranial  pressure,  resulting  in  a  hemorrhagic  softening.  The  rest 
of  the  motor  area  and  the  underlying  white  matter  was  found  normal.  The  supramarginal  and 
angular  gyri,  with  their  associated  white  matter,  were  very  carefully  examined  and  found  normal, 
as  were  the  convolutions  and  white  matter  of  the  occipital  and  temporal  lobes.  The  basal 
ganglia  and  internal  capsules  showed  no  naked-eye  changes.  The  convolutions,  centrum  ovale, 
basal  ganglia,  and  internal  capsule  of  right  cerebral  hemisphere  normal.  The  ventricles  con- 
tained an  excess  of  fluid.  The  brain-stem,  pons,  cerebellum,  and  medulla  showed  no  macro- 
scopic changes.  Microscopic  examination  showed  the  tumor  to  be  a  glioma.  The  third  left 
frontal  convolution,  with  its  associated  white  matter,  was  found  normal. 


478  C1:N  TRAL  NERVOUS  SYSTEM. 

aphasia,  which  appeared  some  years  later,  was  due  to  the  lesion 
found  at  the  foot  of  the  third  left  frontal  o-yrus.  The  pseudo- 
bulbar paralysis  was  doubtless  due  to  the  combined  lesions 
touiul  in  the  trontal  regions  of  both  hemispheres. 

In  Eskeridge's  case  a  vigorous  man,  a  farmer  and  stock- 
raiser  by  occupation  for  the  last  few  years,  began  about  a  year 
ago  to  suffer  from  irregular  attacks  of  a  spasmodic  nature,  dur- 
ing which  he  would  be  dazed  and  temporarily  unable  to  speak. 
Nine  months  later,  when  a  careful  e.xamination  of  his  condition 
was  made,  all  sensory  phenomena  were  found  normal,  and  no 
paresis  or  paralysis  of  any  muscles.  With  the  right  hand  he 
registered  on  the  dynamometer  230;  left,  220.  He  com- 
plained of  some  headache,  which  was  intermittent  and  located 
in  the  front  of  the  head,  more  on  the  left  side  than  on  the  rieht. 
There  was  no  disturbance  of  the  special  senses.  The  fundus 
and  papilla  of  each  eye  were  normal.  There  was  no  sensory 
aphasia.  The  power  of  articulation  was  quite  good,  except  that 
it  was  slow  and  long  words  were  difficult  for  him  to  utter  dis- 
tinctly. He  could  talk,  read  printinor  and  writine  to  himself  or 
aloud,  and  understood  what  he  read.  There  was  no  difficulty 
in  propositionizing,  and  the  movements  of  the  lips  and  tongue 
were  well  preserved,  except  in  uttering  long  and  hard  words  ; 
otherwise  it  was  impossible  to  discover  any  defect  in  speech. 
In  writing,  as  a  rule,  he  formed  his  letters  perfectly,  but  he 
transposed  letters,  words,  phrases,  and  occasionally  sentences, 
so  that  it  was  impossible  to  read  what  he  had  written.  He  had 
formerly  been  a  good  penman,  and  for  two  terms  served  as  bill 
clerk  in  the  House  of  Representadves  of  the  State  Legislature. 
Eskeridge  had  the  patient  under  observation  for  about  two 
months,  and  during  this  time  he  wrote  a  letter  daily.  The  let- 
ters usually  consisted  of  about  eight  or  ten  lines,  and  each  day 
he  spent  two  hours  or  more  in  writing  and  erasing  words  before 
he  could  complete  his  assigned  task.  At  times  he  seemed  to 
recognize  his  mistakes  in  spelling,  and  at  others  he  did  not 
recoQ^nize  them,  or  was  indifferent  to  them.  On  realizingr  a 
mistake  in  spelling  he  would  often  make  a  greater  one  in  trying 
to  correct  it. 

Finally,  it  was  decided  to  recommend  a  surgical  operation  for 


CEREBRAL  LOCALIZATION.  479 

the  removal  of  a  supposed  growth  or  cyst  in  the  left  frontal  lobe. 
On  December  5,  1895,  Clayton  Parkhill  trephined  over  the  foot 
of  the  left  frontal  convolution,  found  and  removed  a  cyst  con- 
taining about  half  an  ounce  of  a  straw-colored  fluid.  The  cyst 
had  destroyed  the  cortex  over  the  area  about  ^  of  an  inch  in 
diameter,  and  extended  into  the  white  substance  of  the  brain  to 
the  depth  of  nearly  an  inch. 

These  cases,  with  a  somewhat  similar  one  described  by  PItres, 
seem  to  prove  the  existence  of  a  separate  and  distinct  cortical 
center  concerned  in  writing,  located  in  the  posterior  part  of  the 
second  left  frontal  convolution,  which  area  is  just  ventral  to  the 
area  for  the  muscles  which  govern  the  finer  movements  of  the 

fingfers  and  hand,  and  having-  the  same  relation  to  writin gf-mo ve- 
to '  o  o 

ments  as  the  motor  speech-center  has  to  speech-movement. 


SENSORY  CENTER  FOR  WRITING. 

Abundant  clinical  evidence  exists  to  prove  that  lesions  of  the 
left  angular  gyrus  frequently  cause  agraphia  ;  *  so  that  the  state- 
ment may  be  made  that  a  sensory  center  exists  which  is  con- 
cerned in  writing,  located  in  the  left  angular  gyrus,  which  center 
affects  the  motor  center  in  a  reflex  manner  by  means  of  an 
association  tract.  Destruction  of  this  tract  in  the  centrum  semi- 
ovale,  or  of  the  center,  will  produce  agraphia.  Lesions  in  the 
angular  gyrus  caused  agraphia  in  five  out  of  twelve  cases  col- 
lected by  Allen  Starr.  When  it  is  remembered  that  in  order  to 
write  it  is  absolutely  necessary  to  call  to  mind  the  memories  of 
the  appearance  of  the  forms  of  letters,  which  memories  are 
stored  in  the  left  angular  gyrus,  it  is  easily  explainable  why 
agraphia  is  produced  by  a  lesion  of  this  gyrus.  Sensory  agra- 
phia is  probably  always  accompanied  by  word- or  mind-blindness. 
A  pure  case  of  sensory  agraphia  has  not  been  recorded. 


■*  The  terra  agraphia   (d,  privative,  without;  '}pa(po(^,  writing)  was  introduced  by  W.  Ogle 
to  denote  an  inability  on  the  part  of  the  patient  to  write. 


48o  CENTRAL  NERVOUS  SYSTEM. 

THE  CENTERS    WHICH    PRESIDE    OVER  THE   HIGHER 
INTELLECTUAL    FACULTIES. 

Both  experimental  and  clinical  research  seem  to  place  the 
centers  which  preside  over  the  higher  intellectual  or  psychic 
faculties  in  the  prefrontal  lobes.  These  centers  include  all  that 
part  of  each  frontal  lobe  placed  in  front  of  the  ascending  frontal 
convolution  and  separated  from  the  latter  by  the  precentral 
sulcus.  It  is  positive  that  the  motor  speech-center  is  located  in 
the  posterior  part  of  the  left  inferior  frontal  gyrus,  and  it  is 
almost  positive  that  the  motor  center  for  writing  is  on  the  same 
side  in  the  posterior  part  of  the  second  frontal  gyrus.  Whether 
or  not,  in  man,  centers  exist  in  the  posterior  part  of  the  superior 
and  middle  frontal  gyri  for  the  movements  of  the  head  and  eyes 
is  not  positively  known,  although  the  experiments  of  Ferrier 
show  that  such  centers  do  exist  in  the  same-named  convolutions 
of  the  monkey's  brain.  Hitzig  long  ago  proved  that  electric 
irritation  of  the  same  area  in  dogs  was  unattended  by  muscular 
movements  or  any  evidence  of  sensory  disturbance.  Later,  he 
found  that  ablation  of  the  same  area  in  the  same  animals  was 
never  followed  by  any  motor  disturbance.  Ferrier  states  that, 
apart  from  the  fact  that  irritation  of  the  roots  of  the  superior 
and  middle  frontal  gyri  is  attended  by  conjugate  deviation  of 
the  head  and  eyes,  with  the  dilatation  of  the  pupils,  irritation  or 
ablation  of  the  remainder  of  the  frontal  lobes  is  not  attended  by 
muscular  movements,  sensory  disturbance,  or  motor  paralysis. 
The  very  interesting  experiments  recently  performed  by  Professor 
Bianchi  on  twelve  monkeys  and  six  dogs,  of  the  removal  of  the 
frontal  lobes,  shows  that  no  perceptible  difference  was  noticed 
in  the  behavior  or  psychic  manifestations  of  animals  in  which 
one  side  of  the  frontal  lobe  was  mutilated,  but  when  both  frontal 
lobes  were  removed,  decided  psychic  changes  were  noted,  such 
as  a  listless  condition  with  an  expression  of  stupidity ;  the 
animals  failed  to  respond  to  familiar  calls,  took  no  notice  of  the 
actions  of  other  monkeys,  and  were  easily  terrorized,  and  when 
in  danger,  offered  no  defense.  They  walked  aimlessly  about 
their  cages  emitting  cries  as  if  afraid  or  angry,  and  when  food 
mixed  with  filth  was  placed  before  them  they  ate  it  with  avidity. 


CEREBRAL  LOCALIZATION.  481 

not  rejecting  the  filth,  and  when  sugar  and  plaster  were  mixed 
they  devoured  it  as  if  it  were  merely  sugar,  thus  showing  that 
their  comparative  judgments  and  memories  were  defective.  Pro- 
fessor Bianchi  believes,  from  the  results  of  his  experiments,  that 
the  frontal  lobes  are  the  seat  of  the  coordination  and  fusion  of 
incoming  and  outgoing  products  of  the  several  sensory  and 
motor  areas  of  the  cortex,  as  well  as  of  the  emotive  states 
which  accompany  all  the  perceptions,  the  fusion  of  which  con- 
stitutes what  has  been  called  the  psychic  tone  of  the  individual. 
Removal  of  the  frontal  lobes  does  not  interfere  with  the  percep- 
tions taken  singly,  but  destroys  the  physiologic  fusion  which  forms 
the  basis  of  the  association,  and  thus  the  physical  basis  underlying 
recollection,  judgment,  and  discrimination  is  destroyed.  The 
results  of  clinicopathologic  observations  on  man  are  confirmatory 
of  the  experiments  of  Professor  Bianchi — namely,  that  the  frontal 
lobes  preside  over  the  higher  intellectual  or  psychic  processes. 
These  studies  prove,  however,  that  decided  mental  deterioration 
results  when  the  lesions  affect  the  prefrontal  region  of  one  side,* 
although  greater  mental  disturbances  occur  when  both  sides  are 

,# affected.  Dr.  R.  J.  Williamson,  in  an  article  entitled  "The 
Symptomatology  of  Gross  Lesion^  (Tumors  and  Abscesses)  In- 

~  volving  the  Prefrontal  Region  of  the  Brain,"  has  reported  five  orig- 
inal cases  and  collected  forty-five  from  literature,  in  which  gross 
lesions  occurred  in  the  prefrontal  region  and  were  attended,  with 
one  exception,  by  marked  mental  changes,  such  as  a  stupid  ex- 
pression,  the  loss  of  the  power  of  attention,  mental  hebetude, 


*  The  following  case  of  tumor  is  of  ejpecial  interest,  because  it  was  completely  localized  to 
the  centrum  ovale  of  the  right  prefrontal  lobe,  and  was  not  attended  by  any  symptoms  save  of 
a  mental  character. 

The  patient  I  was  seen  in  consultation  with  Dr.  John  Morris,  and  presented  the  following 
history :  AparWfrom  occasional  attacks  of  indigestion,  he  had  been  in  good  health  up  to  Feb- 
ruary I,  1898,  at  which  time  it  was  noticed  that  he  acted  strangely  and  was  much  less  talkative 
than  usual.  He  seemed  oblivious  to  his  surroundings,  and  all  his  actions  were  performed  in  a 
slow  and  very  deliberate  manner.  His  appetite  at  times  was  enormous,  and  at  such  times  he 
would  gorge  himself  with  food  to  the  utmost;  he  rarely  vomited.  The  clerks  in  the  post-office, 
where  he  was  employed  as  a  mail-distributor,  had  noticed  that  he  acted  strangely  and  would 
frequently  err  in  distributing  the  mail.  His  whole  mental  condition  seemed  changed  from  that 
of  intellectual  activity  to  that  of  simple  dementia.  He  would  answer  questions  correctly,  but 
would  deliberate,  thus  consuming  much  time  before  giving  the  answers.  His  only  complaint 
was  a  dull  frontal  and  occipital  headache,  more  or  less  continuous.  At  intervals  of  a  few  days 
to  a  week  he  would  lapse  into  a  semiconscious  state,  from  which  he   could    with  difficulty  be 


4S2  CENTRAL  NERVOUS  SYSTEM. 

loss  of  memory,  and  loss  of  spontaneity.  The  patients  would 
take  no  notice  of  their  surroundings,  sleeping  most  of  the  time, 
or  being  in  a  condition  of  semistupor ;  were  very  slow  to  com- 
prehend, and  when  asked  a  question,  would  take  a  long  time 
to  give  the  answer,  although  the  latter  was  usually  correct.  This 
condition  of  slow  cerebration  has  been  aptly  termed  by  Lloyd 
"  inhibition  of  thouc^ht." 

In  an  unreported  case  of  the  author's,  where,  at  the  autopsy, 
lesions  were  found  involving  both  prefrontal  lobes,  there  was 
loss  of  memory,  mental  hebetude,  slow  cerebration,  complete 
loss  of  control  of  the  rectal  and  vesical  reflexes,  and  a  distinct 
ataxic  trait  resemblino-  cerebellar  ataxia.  It  mav  be  noted  here 
that  this  latter  symptom  has  been  frequently  observed  by  Bruns 
in  cases  of  lesions  of  the  prefrontal  lobes. 


THE  CORTICAL  CENTER  FOR  THE  SPECIAL  SENSE  OF   TASTE. 

The  exact  location  of  the  cortical  center  for  the  sense  of  taste 
is  not  known,  although  the  experiments  of  Ferrier  to  determine 
the  location  of  the  olfactory  center  seems  to  prove  that  the 
center  for  taste  is  also  located  in  the  same  recrion  as  that  for 
smell — namely,  in  the  anterior  part  of  the  hippocampal  and  unci- 
nate gyri.  Destruction  of  this  region  of  one  side  produced  a 
loss  of  the  sense  of  taste  on  the  side  opposite  to  the  lesion, 
while  that  to  smell  was  lost  on  the  same  side.  The  sense 
of  taste  is  so  closely  related  to  the  sense  of  smell  in  man  that 
it  seems  very  probable  that  they  are  both  subserved  by  the 

aroused  ;  this  condiiion  would  last  about  twenty-four  hours,  when  he  would  again  appear 
normal,  save  that  his  mental  condition  was  decidedly  worse.  Examination  elicited  no  cranial 
nerve  involvement.  The  optic  discs  were  normal,  as  were  motion  and  sensation.  No  inco- 
ordination existed.  The  reflexes  were  normal  with  the  exception  of  both  patella-tendon  reflexes, 
which  were  absent.  Mis  cerebration  was  decidedly  inactive ;  he  never  conversed  spontane- 
ously. When  questions  were  put  to  him  he  appeared  expressionless  for  quite  a  long  time,  and 
then  would  answer  them  correctly.  He  failed  to  remember  dates,  and  also  the  character  of 
his  food  from  meal  to  meal.  Slow  cerebration  was  the  dominant  symptom  throughout.  He 
died  May  15th ;  autopsy  on  the  l6th.  Brain  normal,  save  that  a  very  vascular  growth  (sar- 
coma) was  found,  which,  with  its  surrounding  area  of  softening,  destroyed  the  centrum  ovale  of 
the  entire  right  prefrontal  lobe. 

In  this  case,  at  least,  although  the  patient  was  right-handed,  nevertheless  the  right  prefrontal 
lobe  was  evidently  as  much  concerned  in  the  elaboration  of  the  higher  mental  processes  as  was 
the  left. 


CEREBRAL   LOCALIZATION. 


same  region.  In  the  author's  case  referred  to  on  the  followine 
page  there  was  a  loss  both  of  the  sense  of  smell  and  taste,  due 
to  the  lesion  (tumor)  destroying  by  pressure  the  function  of  the 
right  hippocampal  and  uncinate  gyri. 


THE  CORTICAL  CENTER  FOR  THE  SPECIAL  SENSE  OF  SMELL. 

The  olfactoi^y  or  cortical  center  for  smell  is  most  probably 
located  in  that  part  of  the  recurved  portion  of  the  hippocampal 
lobule  known  as  the  uncinate  gyrus.  In  this  area  the  olfactory 
tract  ends.  This  seems  proved  by  the  extirpation  experiments 
of  Gudden,  who  found  that,  after  the  olfactory  bulb  of  one  side 
was  removed,  the  gyrus  uncinatus  of  that  side  atrophied.  Zuc- 
kerkandl,  of  Gratz,  has  shown,  from  the  study  of  the  brains  of 
animals  whose  sense  of  smell  is  very  keen  (osmatics),  that  their 
olfactory  bulbs  and  tracts,  as  well  as  the  uncinate  and  hippocam- 
pal gyri,  are  very  large,  and  form,  on  the  basal  surface  of  each 
temporal  lobe,  a  pyriform  swelling  which  is  called  the  lobus  pyri- 
formis.  On  the  contrary,  in  animals  whose  sense  of  smell  is 
not  well  developed  (anosmatics),  the  same  parts  are  very  small 
or  atrophied.  Ferrier  has  proved  that  the  electric  irritation 
of  the  hippocampal  lobule  in  the  monkey,  cat,  dog,  or  rabbit, 
invariably  produced  subjective  olfactory  sensations,  such  as  tor- 
sion of  the  lip  and  nostril  of  the  same  side,  this  reaction  being 
precisely  the  same  as  is  produced  in  these  animals  by  the  direct 
application  to  the  nostrils  of  some  strong  or  disagreeable  odor, 
and  is  evidently  the  outward  or  associated  expression  of  ex- 
cited olfactory  sensation. 

Ferrier  destroyed  extensively  the  temporal  lobe,  Including  the 
anterior  extremity  of  the  hippocampal  gyrus,  in  four  animals,  and 
found,  In  addition  to  other  sensory  disturbances,  a  distinct  loss 
of  the  sense  of  smell  on  the  same  side  as  the  lesion. 

The  very  few  clinical  cases  with  autopsies  that  are  recorded 
indicate  that  in  man  the  cortical  center  for  smell  is  located  in  the 
uncinate  gyrus. 

Allan  McLane  Hamilton  has  reported  a  case  of  epilepsy  in 
which  the  convulsions  were  always  preceded  by  an  aura  of  a 
dlsasfreeable  odor — sometimes  of  smoke  and   sometimes   of  a 


484  CENTRAL  NERVOUS  SYSTEM. 

fetid  smell — without  sensory  disturbances,   in  which,  at   the   au 
topsy,  an  area  of  softening  in  this  region  was  found. 

Griffith  has  reported  a  case  with  a  loss  of  smell  in  the  right 
nostril,  the  autopsy  showing  an  erosion  of  the  right  uncinate 
gyrus. 

Hughlings-Jackson  reported  a  tumor  of  the  right  temporal 
lobe,  the  patient  having  had  paroxysms  with  a  dreamy  state, 
with  warnings  of  a  crude  sensation  of  smell. 

Worcester  cites  a  case  of  a  farmer  who  had  epilepsy,  and  who 
for  several  days  had  hallucinations  of  smell,  such  as  a  room  full 
of  smoke,  or  an  odor  like  alcohol.  At  the  autopsy  there  was 
found  an  area  of  red  softening  in  the  left  uncinate  gyrus. 

In  an  unreported  case  of  the  author's,  in  wdiich  there  was  a 
loss  of  smell  and  taste,  a  large  tumor  was  found  springing  from 
the  anterior  portion  of  the  basal  surface  of  the  right  temporal 
lobe,  including  the  hippocampal  and  uncinate  gyri. 


THE    LOCALIZATION    OF  LESIONS    IN  THE    CENTRUM 

OVALE. 

In  a  previous  chapter  the  general  and  minute  anatomy  of  the 
centrum  ovale  has  been  considered  at  length.  It  was  found  that 
this  apparently  homogeneous  white  mass  consisted  almost  ex- 
clusively of  medullated  nerve-fibers,  which  were  divisible  into 
association,  commissural,  and  projection  systems.  Hence  the 
diagnosis  of  lesions  of  the  centrum  semiovale  depends  upon 
the  result  of  the  partial  or  complete  destruction  and  consequent 
loss  of  function  of  these  fibers.  The  function  of  the  association 
fibers  is  to  associate  the  various  sensory  perceptions  which  are 
received  in  near  or  distant  parts  of  the  cortex  of  the  same  hemi- 
sphere, and  to  form,  by  this  association,  perfect  mental  pictures. 
The  commissural  fibers  bring  the  corresponding  lobes  of  each 
hemisphere  into  harmonious  relation  with  one  another,  while  the 
projection  fibers  of  which  we  have  any  positive  knowledge  are 
those  which  convey  motor  Impulses  from  the  cortex  and  those 
which  conduct  sensory  Impressions  to  the  cortex.  The  devel- 
opment of  this  branch  of  localization  is  the  work  of  the  past 
five  years,  and  has  resulted  from  the  collation  of  a  number  of 


CEREBRAL  LOCALIZATION.  485 

carefully  recorded  cases   by  Starr,   Seguin,  Wernicke,  Freund, 
and  many  others. 

Up  to  the  present  time  several  cases  of  subcortical  tumors 
have  been  successfully  removed,  and  a  few  cases  of  abscess  in 
this  region  have  been  drained.  Lesions  which  are  located  in 
the  centrum  semiovale  near  the  internal  capsule,  owing  to  the 
convergence  of  the  projection  fibers  as  they  enter  the  capsule, 
produce  symptoms  which  may  be  identical  in  character  to  lesions 
in  the  capsule ;  while  lesions  located  in  the  centrum  semiovale 
just  beneath  the  cortex,  owing  to  a  divergence  of  the  projection 
fibers,  produce  symptoms  almost  identical  with  those  produced 
on  or  in  the  cortex. 

There  are  no  symptoms  of  a  general  character  which  abso- 
lutely stamp  the  lesion  as  being  either  cortical  or  subcortical. 
According  to  Seguin,  the  absence  or  late  appearance  of  head- 
ache would  lend  support  to  the  diagnosis  of  a  subcortical  lesion. 
Clinical  experience  does  not  confirm  this  statement. 

A  careful  study  of  the  recorded  cases  of  lesions  in  the  cen- 
trum semiovale  of  the  prefrontal  lobe  shows  that  the  symptoms 
induced  are  identical  in  character  with  those  produced  by  similar 
lesions  of  the  cortex.     Seguin  has  reported  a  case  of  agraphia, 
the  result  of  a   lesion   in  the  centrum  semiovale,   beneath  the 
base  of  the  second  left  frontal  gyrus  ;  and  several  cases  of  motor 
aphasia  have  been  reported  in  which  a  lesion  was  found  beneath 
the  third  left  frontal  gyrus  ;  but  in  none  of  these  cases  have  any 
symptoms  been  present  by  which  the  lesion   could  have  been 
distinguished  from  a  cortical  lesion.      Dejerine  has  reported  two 
cases  of  complete  aphemia  (mutism),  in  both  of  which  lesions 
were   found  in   the  centrum   semiovale,   beneath  the  third  left 
frontal  convolution,  but  involving  the  white  matter  of  the  inferior 
part  of  the  central. gyri. 


LESIONS  OF  THE  CENTRUM  SEMIOVALE  BENEATH  THE 
MOTOR  AREA. 

In  the  motor  area  a  lesion,  either  cortical  or  subcortical,  may 
be  followed  by  paresis  or  paralysis  of  an  arm,  a  leg,  or  the  face, 
on  the  side  opposite  to  the  lesion.     In  the  great  majority  of  the 


486  CENTRAL  NERVOUS  SYSTEM. 

recorded  cases  of  cortical  lesions  convulsions  of  a  Jacksonian 
type  have  preceded  the  weakness  or  paralysis,  while  in  most 
subcortical  lesions  the  paralysis  has  been  very  gradual  in  its 
onset,  and  the  unilateral  convulsions  (Jacksonian)  have  appeared 
after  the  paralysis,  coming  on  late  or  perhaps  not  at  all. 

If  with  this  eradual  mode  of  onset,  to^jether  with  the  late 
appearance  of  partial  or  complete  unilateral  convulsions,  there 
is  added  paresthesia,  followed  by  a  gradually  increasing  anes- 
thesia of  a  limb,  one  may  be  almost  positive  in  diagnosticating 
a  centrum  semiovale  lesion  beneath  the  sensorimotor  area. 

Wernicke  has  proved,  by  the  records  of  several  cases,  that  if 
a  lesion  is  located  in  the  white  matter  (centrum  semiovale)  be- 
neath the  island  of  Reil,  and  destroys  the  association  bundles 
of  fibers  (fasciculus  uncinatus  and  cingulum)  connecting  the 
sensory  receptive  center  in  the  left  temporal  lobe  with  the  motor 
or  emissive  speech-center  in  the  posterior  part  of  the  third  left 
frontal  convolution,  there  will  occur  a  form  of  speech-defect 
called  paraphasia,  or  the  aphasia  of  condiutioji.  Such  patients 
understand  perfectly  what  is  said  to  them  and  can  articulate 
perfectly,  but  they  fail  to  connect  their  ideas  with  the  proper 
words,  and  hence  are  constantly  using  wrong  words. 


CENTRUM  SEMIOVALE  OF  THE  TEMPORAL  LOBE. 

There  are  no  symptoms  whereby  a  lesion  located  in  the  cen- 
trum semiovale  of  the  right  temporal  lobe  (in  the  right-handed) 
can  be  diagnosticated.  If,  however,  the  lesion  be  located  in  the 
white  matter  of  the  left  upper  and  middle  temporal  gyri,  in- 
complete sensory  aphasia  will  occur.  Wernicke  has  shown  that 
total  deafness  central  in  oriorin  is  due  to  a  lesion  in  the  centrum 
semiovale  of  each  temporal  lobe  destroying  the  auditory  tract. 


LOCALIZATION  OF   LESIONS  IN    CENTRUM  OVALE  OF  THE 

PARIETAL  LOBE. 

M.  Allen  Starr  has  proven,  by  the  record  of  four  cases,  that  a 
lesion  in  the  centrum  semiovale  beneath  the  left  angular  gyrus 
may  destroy  the  fibers  which  conduct  sensory  visual  impressions 


CEREBRAL  LOCALIZATION.  487 

from  the  common  sight-center  to  that  gyrus  and  thus  cause 
Incomplete  word-bHndness  (subcortical  alexia).  The  patient 
being  unable  to  read,  if  his  hand  be  made  to  trace  the  letters  by 
the  hand  of  another  person,  or  raised  type  be  used,  can  recog- 
nize the  letters,  he  having  energized  the  visual  perceptive  cen- 
ter (angular  gyrus)  through  his  muscle  and  tactile  sense  percep- 
tions. 

A  lesion  beneath  the  parietal  lobe  will  produce,  the  nearer 
the  lesion  is  located  to  the  cortex,  partial  or  complete  anesthe- 
sia of  a  limb  ;  the  nearer  the  lesion  is  to  the  internal  capsule,  the 
more  general  and  complete  the  anesthesia  will  be.  Von  Mona- 
kow  has  reported  a  case  where  a  lesion  located  in  the  white  mat- 
ter of  the  supramarginal  and  angular  gyri  produced  a  marked 
disturbance  of  muscular  sense  without  the  slightest  paralysis. 


CENTRUM  SEMIOVALE  OF  THE  OCCIPITAL  LOBE. 

Freund  has  shown,  by  a  critical  resume  of  eight  cases,  that 
sensory  optic  aphasia  (the  inability  to  name  objects  although 
the  objects  are  seen  and  recognized)  with  hemianopsia  are  the 
only  symptoms  which  would  enable  one  to  locate  a  lesion  in  the 
centrum  semiovale  of  the  left  occipital  lobe. 


LESIONS  OF  THE   CORPUS  CALLOSUM. 

No  symptoms  are  at  present  known  by  means  of  which  lesions 
in  the  centrum  semiovale  affecting  the  callosal  fibers  can  be  diag- 
nosed. Theoretically,  as  suggested  by  M.  Allen  Starr,  one  would 
expect,  if  these  commissural  fibers  were  destroyed,  an  inability 
to  perform  corresponding  bilateral  movements,  which  would 
occur  only  after  involvement  of  the  fibers  beneath  the  motor 
areas.  This  symptom  has  been  entirely  overlooked  by  most 
observers  that  have  reported  cases  of  lesions  of  the  corpus 
callosum. 


488  CENTRAL  NERVOUS  SYSTEM. 

LOCALIZATION   OF  LESIONS  OF  THE  INTERNAL 

CAPSULE. 

No  symptoms  exist  by  means  of  which  one  can  locate  a  lesion 
in  tJie  anterior  division  of  the  internal  capsule  ventral  to  its 
knee.  Owine  to  destruction  of  the  frontocerebellar  tract,  which 
would  occur  with  such  a  lesion,  one  would  expect  symptoms 
referable  to  the  frontal  lobe  and  cerebellum. 

A  lesion  involvino^  the  anterior  two-thirds  of  the  posterior 
limb  would  destroy  the  motor  tract  and  cause  a  complete  hemi- 
plegia of  the  opposite  side  of  the  body.  In  those  cases  of  hemi- 
plegia where  the  leg  is  most  involved  anesthesia  occurs  more 
commonly,  owing  to  the  proximity  of  its  fibers  to  the  sensory 
tract.  A  lesion  involving  the  posterior  third  of  the  internal 
capsule  would  destroy  the  fibers  of  the  sensory  tract  and  pro- 
duce a  complete  hemianesthesia  of  the  opposite  side.  This 
may  or  may  not  involve  the  loss  of  the  special  senses  on  the 
side  of  the  anesthesia. 


BASAL  GANGLIA. 

Lesions  which  have  been  found  involving  the  corpus  striatum 
or  optic  thalamus  have  induced  no  symptoms  that  could  not  be 
explained  by  encroachment  upon  the  internal  capsule.  In  sev- 
eral reported  cases  of  so-called  pseudobulbar  paralysis  lesions 
have  been  found  in  the  lenticular  nuclei.  In  a  few^  cases  of 
athetosis,  unaccompanied  by  hemiplegia,  lesions  were  found  in 
both  optic  thalami. 


LOCALIZATIONS  OF  LESIONS  OF  THE   CORPORA 
QUADRIGEMINA. 

The  important  connection  of  the  quadrigeminal  bodies  with 
the  visual  and  auditory  paths,  with  the  superior  cerebellar 
peduncles,  and  with  the  nuclei  of  the  ocular  nerves  is  sufficient 
to  indicate  w^iat  a  variety  of  symptoms  one  would  expect  to 
find  should  these  bodies  become  diseased.  Nothnagel  long  ago 
pointed  out  that  only  two  focal  symptoms  occurred,  the  result 


CEREBRAL  LOCALIZATION.  489 

of  such  diseases,  which  were  absolutely  diagnostic.  These 
symptoms  are,  at  first,  a  slowly  increasing  cerebellar  ataxia, 
identical  with  that  occasioned  by  disease  of  the  middle  lobe 
(vermis)  of  the  cerebellum,  and  a  gradually  increasing  but  not 
entirely  symmetric  ophthalmoplegia.  The  ocular  muscles  most 
often  affected  are  the  superior  and  inferior  recti,  but  all  of  them 
may,  in  turn,  become  involved.  According  to  Bruns,  in  lesions 
of  the  corpora  quadrigemina,  the  ophthalmoplegia  most  often 
precedes  the  ataxia ;  this  fact  is  very  valuable  in  differentiating 
lesions  of  these  bodies  from  a  cerebellar  lesion,  in  which  the  ataxia 
is  always  the  first  event  and  the  ophthalmoplegia,  the  result  of 
the  extension  of  the  disease,  is  secondary.  Neurologists  are 
quite  generally  agreed  that  when  the  lesion  involves  the  ante- 
rior corpora  quadrigemina,  we  have,  in  addition  to  the  ophthal- 
moplegia, at  first  a  contraction  of  the  pupils  (irritation  miosis), 
and,  later,  dilatation  of  the  pupils,  with  a  loss  of  the  light  reflex. 
If  the  posterior  bodies  are  also  involved,  deafness  will  occur ; 
this  latter  symptom  is  due  to  the  implication  of  the  lateral  fillet, 
which  is  the  central  auditory  path,  and  is  connected  chiefly  with 
the  opposite  auditory  nuclei. 


LOCALIZATION   OF  LESION   IN    THE   CRURA  CEREBRI. 

Within  each  cerebral  peduncle  are  compressed  a  number  of 
tracts,  the  two  most  important  of  which  are  the  motor  and 
sensory.  Coming  out  of  the  interpeduncular  space  are  the  third 
pair  of  cranial  nerves, — the  motor  oculi, — each  one  of  which 
courses  around  the  peduncle,  reaching  its  ventral  portion. 
Hence  a  circumscribed  lesion  located  in  the  ventral  part  of  the 
crus  cerebri  will  produce,  owing  to  the  destruction  of  the  motor 
tract  and  third  nerve,  a  para-lysis  of  the  muscles  of  the  opposite 
arm,  leg,  and  lower  part  of  the  face,  a  typical  cerebral  hemiplegia, 
and  a  paralysis  of  all  the  muscles  of  the  eyeball  of  the  side  of  the 
lesion,  with  the  exception  of  the  superior  oblique  and  external 
rectus,  producing  external  strabismus,  ptosis,  and  dilatation  of 
the  pupil.  If  the  lesion  is  sufficiently  deep  to  implicate  the 
sensory  tract  (fillet)  of  the  tegmentum,  hemianesthesia  on  the 
side    opposite   to    the   lesion   will   also   occur.     This   symptom, 


490  CENTRAL  NERVOUS  SYSTEM. 

coupled  with  hemiplegia  on  the  same  side  and  third  nerve  par- 
alysis on  the  side  opposite  to  the  hemiplegia,  is  pathognomonic 
of  a  peduncular  lesion. 


LOCALIZATION   OF   LESIONS  IN   THE   PONS  VAROLII. 

Siiiall  unilateral  lesions  in  the  upper  part  of  the  pons  may  be 
so  placed  that  only  a  hemiplegia  of  the  ordinary  type  will  occur, 
which  can  not  be  distinguished  from  that  produced  by  a  lesion 
within  the  internal  capsule.  If,  however,  the  lesion  is  located  in 
the  lower  half  of  the  pons,  a  few  characteristic  symptoms  will 
be  found,  the  more  typical  of  which  is  an  alternate  hemiplegia, 
or  hemianesthesia,  "so-called  crossed  paralysis," — that  is,  a  par- 
alysis of  motion  or  sensation  involving  the  leg  and  arm  on  the 
side  opposite  to  the  lesion,  with  a  complete  facial  paralysis,  per- 
ipheral in  type,  on  the  side  of  the  lesion.  This  type  of  paralysis 
is  due  to  pressure  or  destruction  of  the  motor  or  sensory  tract 
on  the  side  of  the  lesion,  both  of  which  cross  in  the  medulla 
and  supply  the  opposite  side  of  the  body  with  modon  or  sensa- 
tion, together  wMth  destruction  of  the  facial  nucleus,  or  nerve, 
which  supplies  the  facial  muscles  on  the  same  side  as  the  lesion 
and  opposite  to  the  paralyzed  limbs.  If  the  lesion  involves  the 
sensory  nucleus  or  nerve-roots  of  the  trigeminal,  there  is  at  first 
a  numbness,  followed  by  anesthesia  of  the  face  on  the  side  cor- 
responding to  the  lesion,  with  anesthesia  or  motor  paralysis  on 
the  side  opposite  to  the  facial  anesthesia.  Owing  to  implicadon 
of  the  middle  cerebellar  peduncle,  staggering,  or  a  tendency  to 
fall,  may  occur  toward  the  side  of  the  lesion.  Equally  charac- 
teristic of  a  pons  lesion  is  a  paralysis  of  the  abducens  nerve, 
producing  double  vision  and  internal  strabismus  on  the  side  of 
the  lesion,  with  a  hemiplegia  on  the  opposite  side. 

In  acute  destructive  lesions  of  the  pons  above  the  nucleus  of 
origin  of  the  abducens  or  sixth  nerve,  such  as  hemorrhage  or 
thrombosis,  conjugate  deviation  of  the  head  and  eyes  often 
occur,  both  usually  turning  toward  the  paralyzed  side  and  away 
from  the  side  of  the  lesion.  Irritative  lesions  of  the  pons,  such 
as  tumors,  cause  conjugate  deviation  of  head  and  eyes  toward  the 
side  of  lesion.      Bilateral  lesions  of  the  pons  are  not  very  rare  ; 


Fig.  233. — View  from  Before  of  the  Medulla  Oblongata,  Pons  Varolii,  Crura 
Cerebri,  and  other  Central  Portions  of  the  Encephalon  (Natural  size). — 
{Allen  Thomson.) — {From  Qtiaiii's  "Anatomy.''') 

On  the  right  side  the  convolutions  of  the  central  lobe,  or  island  of  Reil,  have  been  left,  together 
with  a  small  part  of  the  anterior  cerebral  convolutions  ;  on  the  left  side  these  have  been 
removed  by  an  incision  carried  between  the  thalamus  opticus  and  the  cerebral  hemisphere. 

V.  The  olfactory  tract  cut  short  and  lying  in  its  groove.  II.  The  left  optic  nerve  in  front  of  the 
commissure.  11^.  The  right  optic  tract.  Th.  The  cut  surface  of  the  left  thalamus  opticus. 
C.  The  central  lobe  or  island  of  Reil.  Sy.  Fissure  of  Sylvius.  XX-  Anterior  perforated 
space,  e.  The  external  corpus  geniculatum.  /.  The  internal  corpus  geniculatum.  h.  The 
hypophysis  cerebri  or  pituitary  body.  (c.  Tuber  cinereum  with  the  infundibulum.  a.  One 
of  the  corpora  albicantia.  P.  The  cerebral  peduncle  or  crus.  III.  Close  to  the  left  oculo- 
motor nerve.      X-   The  posterior  perforated  space. 

The  following  letters  and  numbers  refer  to  parts  in  connection  with  the  medulla  oblongata  and 
pons.  PV.  Pons  Varolii.  V.  The  greater  root  of  the  fifth  nerve.  +•  The  lesser  or 
motor  root.  VI.  The  sixth  nerve.  VII.  The  facial.  VIII.  The  auditory  nerve.  IX. 
The  glossopharyngeal.  X.  The  pneumogastric  nerve.  XL  The  spinal  accessory  nerve. 
XII.  The  hypoglossal  nerve.  CI.  The  suboccipital  or  first  cervical  nerve,  pa.  Pyra- 
mid, o.  Olive,  d.  Anterior  median  fissure  of  the  spinal  cord,  above  which  the  decussa- 
tion of  ■  the  pyramids  is  represented,  c  a.  Anterior  column  of  cord.  r.  Lateral  tract  of 
bulb  continuous  with  c  I,  the  lateral  column  of  the  spinal  cord. 

491 


CEREBRAL  LOCALIZATION.  493 

they  occasion  bilateral  motor  or  sensory  paralysis,  more  or  less 

complete,    usually  accompanied  with    difficult   deglutition  and 
articulation. 


LOCALIZATION   OF  CEREBELLAR  LESIONS. 

Despite  the  numerous  and  important  anatomic  connections 
of  the  cerebellum  with  the  rest  of  the  cerebrospinal  axis,  only 
two  focal  diagnostic  symptoms  exist  by  means  of  which  a  cere- 
bellar lesion  may  be  localized.  These  are,  in  the  order  of  their 
importance,  cerebellar  ataxia,  or  staggering,  and  vertigo.  Cere- 
bellar ataxia,  which  is  a  disturbance  of  equilibrium  in  standing 
or  walking,  occurs  in  two  forms.  In  the  first,  or  common  form, 
most  frequently  observed  in  lesions  of  the  middle  lobe,  or  worm, 
the  gait  is  staggering  ;  the  patient  walks  with  his  feet  wide  apart 
and  sways  from  side  to  side  very  like  a  drunken  man  ;  he  may 
walk  -in  a  zigzag  manner  or  have  a  tendency  to  fall  forward, 
backward,  or  to  one  or  the  other  side.  In  this  form  there  is  no 
loss  of  muscular  sense,  and  Romberg's  symptom  is  usually 
absent.  In  the  second  form,  which  is  very  rare,  the  patient's 
gait  resembles  that  of  locomotor  ataxia.  Closure  of  the  eyes 
increases  the  ataxia,. and  Romberg's  symptom  is  nearly  always 
present. 

Vertigo,  although  a  common  general  symptom  of  cerebral 
disease,  exists  in  no  other  affection  so  early,  or  is  so  constant 
and  intense  as  in  cerebellar  disease.  The  patient  either  feels  as 
if  all  objects  were  turning  around  him  or  as  if  he  were  turning 
around  in  space.  While  cerebellar  ataxia  and  vertigo,  coupled 
with  nystagmus  and  other  general  symptoms  referable  to  brain 
diseases — headache,  vomiting,  optic  neuritis— are  almost  path- 
ognomonic of  a  cerebellar  lesion,  they  do  not  indicate  the  exact 
situation  in  the  cerebellum  of  the  lesion. 


LESIONS  OF  THE    MIDDLE  LOBE,  OR  WORM. 

Lesions  of  this  lobe  are  nearly  always  accompanied  by  the 
most  exquisite  cerebellar  ataxia  combined  with  severe  vertigo. 
Nothnagel  long  ago  pointed  out  that  cerebellar  ataxia  is  always 


494  CENTRAL  NERVOUS  SYSTEM. 

due  to  a  lesion  of  the  middle  lobe  or  is  the  result  of  the  second- 
ary involvement  of  that  lobe  by  the  encroachment  upon  it  of  a 
lesion  which  has  had  its  origin  in  a  cerebellar  hemisphere.  The 
above  statement  of  Nothnagel  is  supported  both  by  Gowers  and 
by  M.  Allen  Starr  ;  the  latter  observer  states  that  the  occurrence 
of  staeeerinor  indicates  that  the  middle  lobe  is  either  the  seat 
of  the  tumor  or  is  encroached  upon  by  a  tumor  in  the  hemi- 
sphere. If  the  ataxia  occurs  early  in  relation  to  the  general 
symptoms,  it  is  the  middle  lobe  in  which  the  tumor  began.  If 
it  occurs  late,  after  months  of  suffering,  the  tumor  has  started 
in  a  cerebellar  hemisphere,  giving  rise  to  general  symptoms,  and 
has  at  last  reached  the  middle  lobe,  producing  the  local  symp- 
toms. 

According  to  Flourens  and  .Renzi,  experimental  destruction 
of  the  anterior  part  of  the  worm,  or  middle  lobe,  causes  an  incli- 
nation to  fall  forward  ;  while  a  lesion  of  the  central  and  posterior 
parts  causes  the  head  to  be  pulled  backward,  with  a  tendency 
to  fall  in  the  same  direction.  Bastian  believes  that  a  tendency 
to  fall  forward  exists  when  the  lesion  involves  the  inferior  worm  ; 
but  when  the  lesion  involves  the  superior  worm,  a  tendency  to 
fall  backward  occurs. 

Several  cases  have  been  recorded  to  support  the  following 
statement  of  Wetzel  and  Bohm — namely,  that  cerebellar  inco- 
ordination, or  ataxia,  only  occurs  in  disease  of  the  posterior  part 
of  the  middle  lobe  ;  when  the  lesion  exists  in  the  anterior  part, 
no  incoordination  occurs. 


LESIONS  OF   THE  CEREBELLAR  HEMISPHERES. 

Lesions  in  either  hemisphere  of  the  cerebellum  only  become 
localizable  when  the  lesion  encroaches  upon  the  middle  lobe  or 
adjacent  parts — crus,  pons,  or  medulla.  The  recent  experiments 
of  Luciani  and  Turner  seem  to  prove  that  when  a  lesion  is 
located  in  a  cerebellar  hemisphere,  paresis  occurs  in  the  extrem- 
ities corresponding  to  the  side  of  the  lesion.  Ferrier,  on  the 
contrary,  states  that  lesions  of  the  cerebellum,  while  interfering 
with  the  mechanical  adjustments  against  bodily  equilibrium,  do 


CEREBRAL  LOCALIZATION.  495 

not  cause  paralysis  of  voluntary  motion.  The  above  statement 
of  Luciani  and  Turner  does  not  seem  to  be  supported  by  clinical 
evidence.  In  most  cases  of  cerebellar  disease  accompanied  by 
motor  weakness  or  paralysis,  this  has  occurred  on  the  side  oppo- 
site to  the  lesion,  the  result  of  pressure  on  the  pyramidal  tract 
above  the  motor  cross-way,  either  in  the  crus,  pons,  or  medulla  ; 
with  this  paresis  or  paralysis  there  is  often  an  exaggeration  of  the 
patella  tendon  reflex,  together  with  ankle-clonus.  The  only 
case  in  man  with  which  I  am  acquainted,  where  paresis  occurred 
on  the  same  side  as  the  lesion,  was  one  of  an  abscess  of  a  cere- 
bellar hemisphere  reported  by  Turner,  The  fact  that  the  patient 
always  staggers  toward  the  same  side  is  of  no  great  clinical 
value  in  locating  the  hemisphere  affected,  as  it  is  impossible  to 
know  whether  the  lesion  be  irritative  or  destructive  in  character. 
Beevor  has  had  two  cases,  in  both  of  which  staggering  occurred 
on  the  side  opposite  to  the  lesion,  in  one  of  which  a  growth  was 
successfully  diagnosed  and  removed. 

Cranial-nerve  symptoms  usually  occur  at  first  on  the  side  of 
the  lesion  ;  hence  internal  strabismus,  facial  paralysis, — either  sen- 
sory or  motor, — deafness,  or  retraction  of  the  head  point  toward 
an  involvement  of  the  cerebellar  hemisphere  on  that  side.  If, 
with  the  late  appearance  of  ataxia,  there  occurs  unilateral  cra- 
nial nerve  involvement,  together  with  hemiplegia  of  the  opposite 
side,  one  may  be  positive  in  locating  the  lesion  in  the  cerebellar 
hemisphere  corresponding  to  the  side  of  the  cranial  nerve 
involvement  and  opposite  to  the  paralyzed  side. 


LESIONS  OF  THE  MIDDLE    CEREBELLAR    PEDUNCLE. 

Experimental  division  in  animals  of  the  middle  cerebellar 
peduncle  results  in  a  rapid  rotation  of  the  animal  around  its 
longitudinal  axis,  and,  according  to  Magendie,  Renzi,  and  Schiff, 
toward  the  side  of  the  section  ;  but,  according  to  Luciani,  away 
from  the  side  of  the  section.  Lesions  in  the  middle  peduncle 
cause  in  man  a  similar  tendency  to  rotation  around  the  long 
axis  of  the  body  and  toward  the  side  of  the  lesion,  together 
with,  as  was  pointed  out  by  Nonat,  a  divergence  of  the  eyes. 


496  CENTRAL  NERVOUS  SYSTEM. 

the  eye  on  the  side  of  the  injury  being  directed  downward  and 
inward,  while  the  eye  of  the  sound  side  is  turned  upward  and 
outward. 


LOCALIZATION   OF    LESIONS    IN    THE   MEDULLA 
OBLONGATA. 

Owing  to  the  proximity,  in  the  ventral  part  of  the  medulla  of 
the  motor  and  sensory  tracts,  and,  in  the  dorsal  part,  of  the 
nuclei  of  the  bulbar  nerves,  small  lesions  usually  cause  bilateral 
symptoms.  In  case  of  a  lesion  in  the  ventral  part  of  the  me- 
dulla, bilateral  motor  and  sensory  paralysis  may  occur.  This 
may  or  may  not  be  associated  with  symptoms  referable  to  the 
involvement  of  the  various  bulbar  nerve-nuclei  in  the  dorsal 
part  of  the  medulla.  A  unilateral  lesion  involving  the  most 
ventral  part  of  the  medulla,  implicating  the  hypoglossal  nerve, 
will  cause  paralysis  of  the  leg  and  arm  on  the  side  opposite  to 
the  lesion,  with  a  unilateral  paralysis  of  the  tongue  on  the  same 
side.  In  case  of  lesions  of  the  dorsal  part  we  get  primarily 
symptoms  referable  to  implication  of  the  bulbar  nerve  nuclei. 
In  lesions  of  sudden  onset,  such  as  hemorrhage  or  vascular 
occlusion,  instantaneous  death  is  likely  to  ensue,  owing  to  the 
obliteration  of  function  of  the  respiratory  and  cardiac  centers. 

The  characteristic  combination  of  symptoms'  diagnostic  of 
lesions  of  the  medulla  are  those  known  under  the  name  of 
labioglossolaryngeal  paralysis.  This  characteristic  form  of 
paralysis  is  due  to  a  very  slowly  progressing  bilateral  degen- 
eration of  the  nerve-cells  of  the  motor  bulbar  nuclei.  This 
degeneration  usually  starts  in  the  nuclei  of  the  hypoglossal 
nerves,  and  in  turn  affects  the  nuclei  of  the  spinal  accessory, 
glossopharyngeal,  pneumogastric,  and,  occasionally,  the  facial. 
As  a  result  of  this  degeneration  the  following  symptoms  occur: 

At  first,  paresis,  followed  by  wasting  and  paralysis  of  the 
muscles  of  the  tongue,  with  difficulty  in  articulation  ;  this  is  soon 
followed  by  weakness  and  wasting  of  the  orbicularis  oris,  and 
usually  of  some  of  the  other  muscles  of  expression,  owing  to 
paralysis  of  the  tongue,  soft  palate,  and  muscles  of  deglutition  ; 
mastication  and  deglutition  become  very  difficult,  liquids  being 


CJT 


C.VZ 


Fig.  234  A. — Diagram  of   Skin  Areas  Corresponding  to  Different  Spinal  Seg- 
ments.— [From  Tysoti,  after  Starr.) 
32  497 


en 


c^/^ 


Fig.  234  B. — Diagram  of  Skin  Areas  Corresponding  to  Different  Spinal  Seg- 
ments.—  {From  Tyson,  after  Starr.) 
498 


CEREBRAL  LOCALIZATION.  499 

frequently  regurgitated  through  the  nose.  As  a  result  of  the 
involvement  of  the  nuclei  of  the  spinal  accessory  nerves,  laryn- 
geal symptoms  supervene,  such  as  weakness  of  the  voice,  diffi- 
culty in  coughing,  and  marked  difficulty  in  phonation.  Because 
of  the  paralysis  of  the  epiglottis,  particles  of  food  frequently 
lodge  in  the  larynx  or  bronchi,  often  giving  rise  to  insufflation 
pneumonia. 

There  is  a  rare  form  of  bulbar  paralysis  acute  in  onset,  prob- 
ably of  an  infectious  nature,  accompanied  by  the  same  symp- 
toms as  previously  described,  only  being  much  more  rapid  in  their 
development,  death  usually  resulting  within  a  few  weeks.  This 
affection  resembles  acute  poliomyelitis  of  children,  but  the  prog- 
nosis is  much  more  grave. 

In  many  cases  of  tumor  involving  the  medulla  oblongata  dia- 
betes mellitus,  polyuria,  bradycardia,  tachycardia,  and  Cheyne- 
Stokes  respiration  have  been  observed,  in  addition  to  the  before- 
mentioned  symptoms. 


LOCALIZATION  OF  SPINAL-CORD   LESIONS. 

The  symptoms  available  for  diagnosis  and  localization  of 
spinal-cord  diseases  may  be  divided  into  two  great  groups, — 
motor  and  sensory, — corresponding  in  a  general  way  to  the 
ventral  and  dorsal  parts  of  the  cord. 

The  motor  symptoms  may  be  due  to  affections  of  the  upper 
(corticospinal)  or  lower  (spinomuscular)  motor  neurones,  each 
of  which  produces  a  perfectly  distinct  and  classic  type  of  par- 
alysis. If  the  upper  motor  neurones  are  separated  at  any  part 
of  their  course  from  their  trophic  cells  in  the  motor  area  of  the 
cerebral  cortex,  there  results  a  secondary  degeneration  down- 
ward, involving  the  direct  and  crossed  pyramidal  or  motor  tracts, 
which  gives  rise  to  a  type  of  paralysis  having  the  following 
characters :  All  the  muscles  are  equally  involved,  though  the 
limbs  are  incompletely  paralyzed.  The  muscles  are  usually  not 
wasted,  save  from  disuse,  and  they  are  continually  in  a  state  of 
partial  or  complete  tonic  contraction,  giving  rise  to  stiffness  and 
rigidity.     The  electric  reactions  are  normal  ;  muscular  irritability 


500 


CENTRAL  NERVOUS  SYSTEM. 


I  C 


is  greatly  increased,  the  slightest  tap  producing  prompt  muscular 
contraction  ;  the  reflexes,  both  superficial  and  deep,  are  greatly 

exaggerated,  ankle-  and  knee-clonus 
being  usually  present.  As  a  result  of 
this  form  of  paralysis,  locomotion  is 
much  interfered  with  and  a  character- 
■^  istic  spastic  gait  is  developed.  The 
patient  assists  himself  with  two  canes  ; 
^        his    chest    is    bent    forward  ;    the    legs 

7  move  forward  very  stiffly  by  the  aid  of 

8  the  trunk-muscles,  the  toes  scraping 
iD  the  ground,  and  the  knees  frequently 
"  interlockinof — cross-le^>"^ed  progression. 
^  \  ery  rarely  cases  occur  in  which  a 

primary    degeneration     of    the     motor 

tracts  in   the   cord   (spinal  part  of  the 

corticospinal    tracts)    has    been    found 

with    symptoms   identical    in    character 

with  those  previously  described.     This 

^        very  chronic  disease  was  first  described 

lo       by  Erb  in  1875,  and  is  generally  known 

I '       as  Erb' s  palsy,  primary  lateral  sclerosis, 

y  1 1 |j^I!L- -  —  '  -       or  spasmodic  paralysis. 


^y 


JO 


3 


12 


L/ 


Co. 


I  L 


—  Co. 


I'iG.  235. — 1)i.\(;k.\m  (Fr.\mEd  fro.m  an  Original 
Investigation)  Showing  the  Relation  of  the 
Vertebral  Spjnes  to  Their  Bodiks  and  to  the 
Origin  of  the  Several  Nerve-roots. — {After 
Gowers. ) 

It  will  be  seen  tliat  the  ends  of  the  vertebral  .spines  are 
opposite  the  middle  of  their  own  bodies  only  in  the  lum- 
bar region  ;  they  correspond  to  the  lower  edge  of  their 
own  bodies  in  the  cervical  and  the  last  two  dorsal  verte- 
brae, and  to  the  upper  part  of  the  body  below  in  the  rest 
of  the  dorsal  region.  Each  cervical  spine  is  nearly  op- 
posite the  lower  roots  of  the  nerve  below.  The  vertebra 
prominens  is  opposite  the  first  dorsal  roots,  and  from  the 
third  to  the  tenth  dorsal  the  spines  correspond  to  the 
second  root  below ;  the  eleventh  spine  corresponds  to 
the  first  and  second  lumbar  nerves,  the  twelfth  to  the 
third,  fourth,  and  fifth  ;  the  first  lumbar  to  the  first, 
second,  and  third  sacral  nerves,  while  the  top  of  the  cord 
is  opposite  the  upper  part  of  the  second  lumbar. 


CEREBRAL  LOCALIZATION.  501 

When  the  lower  or  spinomuscular  neurones  are  affected,  there 
results  a  paralysis  of  another  type,  equally  characteristic,  and 
easily  recognized.  In  this  form  all  the  muscles  of  a  limb  or 
limbs,  or,  what  is  more  common,  only  certain  -groups  of  muscles, 
are  involved.  The  muscles  are  completely  paralyzed,  are  very 
flabby,  become  atrophied,  and  present  the  reaction  of  degenera- 
tion, with  usually  a  loss  of  the  deep  reflexes.  The  hmbs  never 
become  stiff;  contractures,  however,  are  frequent.  This  form 
of  paralysis  is  always  due  to  disease  of  the  cells  of  the  peripheral 
motor  neurones  in  the  anterior  horns  of  the  spinal  cord.  The 
most  common  type  of  this  disease  is  infantile  spinal  paralysis 
Q^c  poliomyelitis  anterior  acuta.  When  these  motor  cells  become 
slowly  degenerated,  there  occurs  a  typical  form  of  spinal-cord 
disease  knows  as  progressive  miisrular  atrophy  ;  in  this  disease 
there  occurs  a  very  gradual  wasting  of  the  muscles  in  an  orderly 
manner,  beginning  usually  in  the  muscles  of  the  ball  of  the  thumb 
and  interossei,  or  about  the  shoulder,  and  gradually  involving 
the  muscles  throughout  the  body.  In  amyotrophic  lateral  sclerosis 
there  is  a  combination  of  muscular  wasting  and  spasmodic 
rigidity,  very  gradual  in  its  progress,  the  wasting  usually  involv- 
ing the  muscles  of  the  upper  extremities,  and  the  weakness  and 
rigidity  the  lower.  This  disease  indicates  symmetric  bilateral 
lesions  of  both  the  central  and  peripheral  motor  neurones.  It 
is  really  a  combination  of  the  symptoms  of  progressive  muscular 
atrophy  in  addition  to  those  of  spinal  spastic  paralysis,  or 
lateral  sclerosis. 

The  sensory  symptoms  due  to  lesions  of  the  spinal  cord  are 
disturbances  of  pain,  tactile,  temperature,  and  muscular  senses. 
These  various  forms  of  sensory  impressions  are  conveyed 
brain  ward  by  the  sensory  tracts  of  the  cord.  While  much 
doubt  exists  as  to  the  exact  paths  for  their  conduction,  it  is 
highly  probable  that  pain  and  temperature  sense  impressions  are 
conducted  by  Gowers'  anterolateral  ascending  tract  on  the  side 
opposite  to  their  point  of  entrance,  the  sensations  being  carried 
by  collaterals  from  axones  of  the  cells  of  the  posterior  spinal 
ganglia  (posterior  nerve-roots)  to  cells  existing  in  the  central 
gray  matter  of  the  same  side,  the  impulses  being  further  con- 
veyed by  the  axones  of  these  latter  cells   through  the  anterior 


502  CENTRAL  NERVOUS  SYSTEM. 

commissure  to  Gowers'  tract  of  the  opposite  side.  A  lesion, 
then,  of  the  central  yray  matter  usually  causes  a  loss  ot  both  of 
these  senses,  producing^  analgesia  and  thermo-anesthesia  on  one 
or  both  sides.  Tactile  and  muscular  sense  impressions  are  con- 
veyed via  the  posterior  nerve-roots  into  the  posterior  columns  ; 
the  muscular  sense  impressions  pass  upward  on  the  same  side, 
while  the  tactile  pass  across  and  upward  on  the  opposite  side; 
hence  a  lesion  of  the  posterior  columns  will  produce  anesthesia 
and  ataxia  of  one  or  both  sides.  The  function  ot  the  direct 
cerebellar  tract  is  not  known,  although  most  observers  agree 
witli  Flechsig — that  it  also  conducts  muscular  sense  impres- 
sions. Owing  to  the  fact  that  all  forms  of  sensation  are 
conveyed  to  the  cord  by  means  of  the  posterior  nerve-roots, 
a  lesion  of  these  roots  at  their  junction  with  the  cord,  or  in  the 
columns  of  Burdach.  will  occasion  at  first  irritative  symptoms, 
paresthesia,  neuralgic  pains,  ataxia,  and,  later,  anesthesia,  anal- 
gesia, and  thermo-anesthesia.  These  symptoms  may  come  on 
rapidly,  the  result  of  pressure  from  a  new  growth,  when  they  are 
at  first  unilateral,  or  the)-  may  appear  very  gradually  from  a 
slowly  progressing  degeneration,  as  in  locomotor  ataxia,  when 
they  are  bilateral. 

The  symptoms  of  this  latter  affection  are  so  characteristic  of 
degeneration  of  the  posterior  nerve-roots  and  columns  that  they 
will  be  enumerated  here.  In  the  early  stage  very  severe  pains 
occur,  stabbing  or  neuralgic  in  character ;  also  various  forms 
of  sensory  disturbances  included  under  the  head  of  paresthesia. 
Loss  of  patella  tendon  reflexes  and  of  the  reflex  contraction  of 
the  pupils  to  light  are  among  the  earliest  symptoms.  In  the 
second  stage  all  of  these  symptoms  are  continued  and  exagger- 
ated, and  there  is  added  marked  incoordination  or  ataxia,  with 
local  areas  of  anesthesia  and  analgesia,  retardation  to  the  con- 
duction of  painful  impressions,  and  a  gait  more  or  less  charac- 
teristic,— the  patient  usually  walks  with  the  aid  of  canes,  his 
eyes  being  fixed  on  his  feet  in  order  to  guide  their  movements, 
which  are  irregular  and  jerky,  the  feet  flying  outward  and  the 
heels  coming  dowm  to  the  ground  with  a  stamp.  In  the  third 
stage  the  lesion  involves  the  anterior  horns,  and  there  is  added 
muscular  atrophy  with  paralysis  of  the  extremities. 


CEREBRAL.  LOCALIZATION. 


503 


Syringomyelia,  which  is  a  disease  resulting  in  cavity  forma- 
tion in  the  central  gray  matter  of  the  cord,  is  characterized  by 
the  symptoms  of  progressive  muscular  atrophy,  spinal  in  type, 
with  sensory  and  vasomotor  disturbances, — chiefly  analgesia  and 
thermo-anesthesia, — the  first  beine  due  to  a  destruction  of  the 


XIID 


Fig.  236. — Diagram  of  Lesion  Showing  Brown- 
Sequard's  Paralysis. — lyAfter  Starr,  frof/i 
Tyson?] 

L.  Lesion  in  left  half  of  cord  cuts  off  motor  impulses 
to  left  leg,  sensory  impulses  from  right  leg,  and 
sensory  impulses  from  eleventh  dorsal  nerve. 


Fig.  237. — Schema  Showing  Chief 
Symptoms  in  Left  Unilateral 
Lesion  of  the  Dorsal  Cord. — 
[After  Erb,from  Tyson.') 

Oblique  shading  signifies  motor  and 
vasomotor  paralysis;  vertical,  cuta- 
neous anesthesia ;  dots,  cutaneous 
hyperesthesia,  b.  Small  anesthetic 
zone.     c.   Small  hyperesthetic  zone. 


motor  cells  of  the  anterior  horns,  and  the  latter  being  due  to 
the  destruction  of  the  cells  of  origin  or  fibers  of  Gowers'  tract. 
There  is  an  affection  of  the  cord  known  as  ataxic  paraplegia, 
characterized  clinically  by  weakness,  ataxia,  and  an  increase  of 
the  reflexes,  and  pathologically  by  a  slow-going  degeneration  or 
sclerosis  of  the  lateral  and  posterior  columns. 


504  CENTRAL  NERVOUS  SYSTEM. 

The  symptoms  due  to  a  unilateral  lesion  of  the  cord  are  hyper- 
esthesia, motor  paralysis,  and  incoordination  on  the  side  of  the 
lesion,  with  a  loss  of  tactile,  painful,  and  temperature  senses  on 
the  side  opposite  to  the  lesion.  This  combination  of  symptoms 
is  called  Brozvn-Scquaj-d' s  paj-alysis  (I'igs.  236  and  237). 

In  complete  transverse  lesions  of  the  cord  (myelitis,  hemor- 
rhage, traumatism)  in  the  cervical  rcoion  there  will  occur  at  first 
a  total  paralysis  of  motion,  and  usually  of  sensation  in  the 
arms  and  legs  and  the  trunk,  with  a  subsequent  atrophy  of  the 
muscles  innervated  by  the  cells  of  the  anterior  horns  destroyed 
by  the  lesion,  the  anesthesia  existing  as  high  as  the  level  of 
the  lesion.  The  reflexes  of  the  upper  extremities  will  probably 
be  lost,  whereas  those  of  the  lower  extremities  will  be  exagger- 
ated, ankle-  and  knee-clonus  present ;  the  bladder  and  rectum 
are  paralyzed.  In  the  dorsal  region  the  upper  extremities  escape, 
but  paralysis  of  motion  and  sensation  exists  below  the  level  of 
the  lesion — the  reflexes  are  exaggerated.  In  the  lumbar  region 
paralysis  of  motion  and  loss  of  sensation  occurs  below  the  level 
of  the  lesion  ;  if  in  the  upper  part  the  patella  tendon  reflexes 
are  lost,  ankle-clonus  may  be  present ;  here,  also,  as  in  the  cervi- 
cal regions,  the  muscles  become  wasted,  owing  to  the  destruction 
of  the  cells  of  the  anterior  horns  (peripheral  motor  neurones). 

In  the  sacral  region  incomplete  paraplegia,  incomplete  sensory 
paralysis,  anesthesia  of  the  outer  parts  of  each  lower  extremity,  as 
well  as  the  perineum  and  scrotum,  occur,  together  with  paralysis 
and  anesthesia  of  the  bladder  and  rectum.  No  ankle-clonus  is 
present.      Patella  reflexes  may  be  present. 

In  reeard  to  the  diagnosis  of  the  exact  location  and  extent  of 
any  spinal-cord  lesion,  recourse  may  be  had  to  the  excellent 
table  prepared  by  Starr,  which  is  appended  to  the  text.  These 
are  the  result  of  the  study  of  a  large  number  of  spinal-cord 
lesions  with  autopsies,  in  which  the  same  location  of  the  lesion 
produced  the  same  symptoms.  It  must  be  remembered  that  the 
peripheral  sensory  nerves  anastomose  so  freely  that  to  get  a 
total  anesthesia  of  any  part  of  the  skin,  the  sensory  fibers  from 
two  adjacent  segments  of  the  cord  must  be  destroyed. 


CEREBRAL  LOCALIZATION. 


505 


LOCALIZATION  OF  THE  FUNCTIONS  OF  THE  SEGMENTS  OF  THE 

SPINAL   CORD.— (^//^^  M.   Alien  Starr.) 


Segment. 


II.  and  III. 
C. 


IV.  C. 


Sternomastoid. 
Trapezius. 
Scaleni  and  neck. 
Diaphragm. 


Diaphragm. 

Deltoid. 

Biceps. 

Coracobrachialis. 

Supinator  longus. 

Rhomboid. 

Supra-  and  infraspinatus. 


Reflex. 


Hypochondrium  (?). 

Sudden  inspiration  pro- 
duced by  sudden  pressure 
beneath  the  lower  border 
of  ribs. 


Pupil,  fourth  to  seventh  cer- 
vical. 

Dilatation  of  the  pupil  pro- 
duced by  irritation  of 
neck. 


Sensation. 


Back  of  head  to  vertex. 
Neck. 


Neck. 

Upper  shoulder. 

Outer  arm. 


V.  C. 


VI.  C. 


Deltoid. 

Biceps. 

Coracol^rachialis. 

Brachialis  anticus. 

Supinator  longus. 

Supinator  brevis. 

Rhomboid. 

Teres  minor. 

Pectoralis  (clavicular  part). 

Serratus  magnus. 


Biceps. 

Brachialis  anticus. 
Pectoralis  (clavicular  part). 
Serratus  magnus. 
Triceps. 

Extensors  of  wrist  and  fin- 
gers. 
Pronators. 


Scapular. 

Fifth  cervical  to  first  dorsal. 

Irritation  of  skin  over  the 
scapula  produces  contrac- 
tion of  the  scapular  mus- 
cles. 

Supinator  longus. 

Tapping  its  tendon  in  wrist 
produces  flexion  of  fore- 
arm. 


Triceps. 

Fifth  to  sixth  cervical. 

Tapping  elbow  tendon  pro- 
duces extension  of  fore- 
arm. 

Posterior  wrist. 

Sixth  to  eighth  cervical. 

Tapping  tefidons  causes  ex- 
tension of  hand. 


Back    of    shoulder    and 

arm. 
Outer    side  of  arm  and 

forearm,       front      and 

back. 


Outer    side    of  forearm, 

front  and  back. 
Outer  half  of  hand. 


VII.  C.     I  Triceps  (long  head). 

Extensors  of  wrist  and  fin- 
gers. 
Pronators  of  wrist. 
Flexors  of  wrist. 
Subscapular. 
Pectoralis  (costal  part). 
Latissimus  dorsi. 
Teres  major. 


VIII.  C. 


Flexors  of  wrist  and  fingers. 
Intrinsic  muscles  of  hand. 


Anterior  wrist.  ;  Inner  side  and  back  of 

Seventh  to  eighth  cervical.  !     arm  and  forearm. 

Tapping    anterior    tendons    Radial  half  of  the  hand, 
causes  flexion  of  wrist. 

Palmar.      Seventh    cervical 
to  first  dorsal. 

Stroking  palm  causing  clos- 
ure of  fingers. 


Forearm  and  hand,  inner 
half. 


I.  D. 


Extensors  of  thumb. 
Intrinsic  hand  muscles. 
Thenar      and      hypothenar 
eminences. 


II.  to  XII. 
D. 


Muscles  of  back  and  abdo-  '  Epigastric.  Fourth      to 

men.  !     seventh  dorsal. 

Erectores  spince.  Tickling  mammary  region 

causes    retraction    of  the 
epigastrium. 
Abdominal.        Seventh    to 

eleventh  dorsal. 
Stroking  side  of  abdomen 
causes  retraction  of  belly. 


Forearm,  inner  half. 
Ulnar     distribution      to 
hand. 

Skin  of  chest  and  abdo- 
men, in  bands  running 
around  and  downward 
corresponding  to  spinal 
nerves. 

Upper  gluteal  region. 


5o6 


CENTRAL  NERVOUS  SYSTEM. 


LOCALIZATION  OF  THE  FUNCTIONS  OF  THE  SEGMENTS  OF  THE  SPINAL 

CORD.— {Con/inue</.) 


Segment. 


I.  L. 


II.  L. 


III.  L. 


Muscles. 


Iliopsoas. 
Sartorius. 
Muscles  of  abdomen. 


Iliopsoas.     Sartorius. 
Flexors  of  knee  (Remak). 
Quadriceps  femoris. 


Reflex. 


Sensation. 


Quadriceps  femoris. 
Inner  rotators  of  tliitjh. 
Abductors  of  thijrh. 


IV.  L. 


Abductors  of  thigh. 
Adductors  of  thigh. 
Flexors  of  knee  (Ferrier) 
Tibialis  anticus. 


Cremasteric.     First  to  third    Skin  over  groin  and  front 
lumbar.  of  scrotum. 

Stroking  inner  thigh  causes 
retraction  of  scrotum. 

Patella  tendon.  Outer  side  of  thigh. 

Striking  tendon  causes  ex- 
tension of  leg. 


Front  and  inner  side  of 
tliish. 


Gluteal.  I  Inner  side  of  thigh  and 

Fourth  to  fifth  lumbar.  leg  to  ankle. 

Stroking      buttock     causes    Inner  side  of  foot. 
dim[)ling  in   fold  of  but- 
tock. 


V.  L.         Outward  rotators  of  thigh. 
Flexors  of  knee  (Ferrier). 


Flexors  of  ankle. 
Extensors  of  toes. 


I.  to  II.  S. 


III.  to  V. 

S. 


Flexors  of  ankle. 

Long  flexor  of  toes. 

Peronei. 

Intrinsic  muscles  of  foot. 


Back  of  thigh,  back  of 
leg,  and  outer  part  of 
foot. 


Plantar.  Back  of  thigh. 

Tickling  sole  of  foot  causes    Leg  and  foot,  outer  side, 
flexion  of  toes  and  retrac- 
tion of  leg. 


Perineal  muscles. 


Foot  reflex.     Achilles  ten-    Skinoversacrum.  Anus. 

don.  Perineum.     Genitals. 

Overextension  of  foot  causes 

rapid      flexion  ;       ankle- 
•   clonus. 
Bladder  and  rectal  centers. 


The  Divisions  of  the  Cerebral  Cortex  According  to 
Flechsig. — Flechsig  has  shown  from  the  investigation  of  the 
embryonic  cerebrum  that  the  fibers  of  the  sensory  paths  are  the 
first  to  receive  their  myelin,  the  fibers  of  each  path  developing  one 
after  the  other,  beginning  with  the  fibers  conducting  olfactory 
sensations  and  ending  with  those  carrying  auditory  impressions. 
By  this  study  blechsig  has  shown  that  these  developing  paths 
terminate  in  four  distinct  cortical  areas  or  spheres,  which  have 
received  from  him  the  name  of  projection  or  sensory  spheres  ; 
these  areas  occupy  about  one-third  of  the  whole  cortex,  the 
remaining  two-thirds  being  devoid  of  fibers  of  projection,  but 
contain  fibers  of  association,  which  develop  or  ripen  (become 
medullated)  after  birth,  and  serve  to  connect  the  projection  or 
sensory  spheres  with  the  centers  of  association.     Flechsig  has, 


CEREBRAL  EOCALIZATION.  .  5°? 

therefore,  divided  the  human  cerebral  cortex  into  two  great 
divisions — the  projection  or  sensory  spheres  and  the  centers  of 
association. 

The  projection  or  sensory  spheres  include,  first,  the  tactile 
sphere,  or  somesthetic  area,  which  occupies  the  entire  region 
between  the  fossa  Sylvii  up  to  the  corpus  callosum,  and  includes 
the  central  convolutions,  the  paracentral  lobule,  and  the  dorsal 
parts  of  the  three  frontal  gyri  and  the  middle  third  of  the  gyrus 
fornicatus.  In  this  area  the  fibers  of  the  median  fillet  or 
lemniscus  terminate,  conducting  all  sensations  which  inform  us 
of  the  condition  of  the  body.  This  area  also  includes  the  great 
motor  region,  from  which  arise  all  voluntary  motor  impulses. 

The  olfactory  sphere  includes  the  trigonum  olfactorium,  the 
anterior  perforated  space,  and  the  uncinate  gyrus,  w^hich  is  in 
contact  with  the  island  of  Reil,  and  the  adjacent  hippocampal 
gyrus. 

The  visual  sphere  includes  that  part  of  the  median  surface  of 
the  brain  borderine  on  the  calcarine  fissure  and  about  which 
terminates  the  optic  tract. 

The  auditory  sphere  includes  the  transverse  temporal  gyri, 
about  which  terminates  (lateral  fillet)  the  auditory  tract. 

The  zones  or  centers  of  association  consist  of  three  distinct 
areas :  First,  the  posterior  associaUon  center,  composed  of  the 
lingual,  the  fusiform,  the  parietal,  and  the  inferior  temporal 
convolutions,  together  with  anterior  part  of  the  outer  surface  of 
the  occipital  lobe  ;  second,  the  median  associadon  center,  con- 
sisting-^ of  the  island  of  Reil;  third,  the  anterior  association 
center,  which  consists  essendally  of  the  prefrontal  lobes. 
Flechsie  believes  that  these  centers  of  associadon  are  the  areas 
of  the  cerebral  cortex  which  are  concerned  in  the  higher  intel- 
lectual faculdes — memory,  judgment,  and  reason. 


CHAPTER    XIII. 

THE  EMBRYOLOGY  OF  THE   CENTRAL   NERVOUS 

SYSTEM. 

Very  early  in  embryonic  life — about  the  age  of  twenty-four 
hours  in  the  chicken — there  occurs  in  the  epiblast  a  central  axial 
portion,  the  so-called  medullary  plate,  which  soon  becomes  much 
thickened  along  its  sides,  forming  longitudinal  ridges, — the 
medullary  ridges  or  folds.  The  trough-like  space  between  the 
ridges  is  called  the  medullary  groove.  The  medullary  folds 
continue  to  grow  dorsally,  and,  arching  over  the  medullary 
groove,  fuse  with  each  other  at  the  mid-dorsal  line,  thus  con- 
verting the  groove  into  a  canal  called  the  neural  tube  or  canal. 
This  canal  early  presents  at  its  cephalic  end  three  vesicular 
enlargements,  separated  by  corresponding  constrictions.  These 
enlargements  are  the  primary  cerebral  vesicles,  from  which  the 
encephalon  is  developed.  The  remainder  of  the  canal  is  of  a 
uniform  diameter  and  goes  to  form  the  spinal  cord.  By  the 
proliferation  of  the  cells  surrounding  the  neural  tube,  or  canal, 
the  integral  parts  of  the  central  nervous  system  become  devel- 
oped, the  canal,  much  reduced  in  size,  remaining  to  form  the 
central  canal  of  the  spinal  cord  and  the  ventricles  of  the  brain. 
Thus  it  is  seen  that  the  entire  nervous  system  is  epiblastic  in 
oriofin. 

The  brain  is  developed  from  the  three  primary  cerebral  vesi- 
cles, called,  respectively,  the  anterior  primary  vesicle,  or  fore-brain  ; 
the  middle  primary  vesicle,  or  mid-brain;  and  the  posterior 
primary  vesicle,  or  hind-brain.  This  latter  vesicle  soon  becomes 
much  thickened  on  the  anterior  part  of  the  dorsal  wall,  to  form 
the  cerebellum  ;  this  unequal  development  dividing  this  vesicle 
into  two  parts,  called  the  fourth  and  fifth  cerebral  vesicles,  or  the 

508 


Fig.  238. — Sections  Showing  Stages  in  the  Conversion  of  the  Medullary  Groove 
INTO  the  Neural  Canal.     From  the  tail  end  of  an  embryo  of  the  cat. — {E.  A.  S., 
from  Qtiaiii.) 
ep,ine,hy.    Epiblast,  mesoblast,  and  hypoblast,     m.g.   Medullary  groove.      «.ir.  (in  IV).   Neural 
canal,      ch.   Notochord.     cce.   Celom.      am.   Tail-fold  of  the  amnion. 

509 


EMBRYOLOGY   OF    THE    CENTRAL    NERVOUS    SYSTEM. 


511 


epencephalon,  and  the  metencephalon  or  myelencephalon.  From 
the  former  is  developed  the  cerebellum  and  pons  Varolii,  while 
from  the  latter  is  developed  the  medulla  oblongata. 

The  first  primary  vesicle,  or  fore-brain,  also  becomes  divided 
into  two  parts  by  a  process  of  budding,  which  starts  from  its 
anterior  wall  as  a  single  small  vesicle,  whose  or^owth  is  exceed- 
ingly  rapid  and  chiefly  in  an  upward  and  dorsal  direction.  From 
this  vesicle  is  developed  the  cerebrum.  It  is  called  the  prosen- 
cephalon, while  the  posterior  part  of  the  primary  vesicle,  or  fore- 
brain,  is  now  called  the  diencephalon,  thalamencephalon,  or  inter- 


FiG.  239. — Longitudinal  Section  of  Head  of  a  Four-and-a-Half-Day  Chick.  The 
five  brain-vesicles  are  fairly  well  developed. — [Afte?-  von  Mihalkovics,  fi'oni  Edinger.) 

I.  Pineal  gland.  2.  Posterior  commissure.  3.  Corpora  quadrigemina.  4.  Cerebellum.  5. 
Fundament  of  the  hypophysis.  6.  Cerebral  cavity.  7.  Thalamencephalic  cavity,  or  third 
ventricle.  8.  Aqueductus.  9.  Cerebellar  cavity.  10.  Cavity  of  medulla.  The  last  two 
together  form  the  fourth  ventricle. 


brain.  There  are  thus  formed,  by  the  division  of  the  primary 
fore-brain  and  the  hind-brain  into  two  parts,  five  secondary 
cerebral  vesicles,  the  central  cavities  of  which  communicate  with 
one  another.  They  are  as  follows:  First,  the  secondary  fore- 
brain,  or  prosencephalon  ;  second,  the  remains  of  the  original  pri- 
mary fore-brain,  now  called  thalamencephalon,  or  'tween-brain ; 
third,  the  mesencephalon,  which  is  the  unaltered  second  or  mid- 
dle primary  vesicle,  or  mid-brain  ;  fourth,  the  epencephalon,  or 
hind-brain  ("  Nachhirn  ")  ;  and,  fifth,  the  metencephalon,  or  after- 


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512 


EMBRYOLOGY  OF   THE   CENTRAL   NERVOUS   SYSTEM.  513 

brain.  The  subjoined  table,  from  Dejerine,  indicates  the  differ- 
ent parts  of  the  cerebrospinal  system  derived  from  each  en- 
cephalic vesicle. 


THE  DEVELOPMENT  OF  THE  SPINAL  CORD. 

That  part  of  the  neural  tube  not  concerned  in  the  formation 
of  the  cerebral  vesicles  is  converted  into  the  spinal  cord.  This 
tube  is  oval  on  cross-section,  and  can  very  early  be  differen- 
tiated into  a  right  and  a  left  half  by  a  thickening  due  to  cell- 
growth  or  multiplication  of  its  lateral  walls.  The  upper  and 
lower  walls,  or  the  roof  and  floor,  remain  very  thin  and  form 
later  the  commissures,  the  former  forming  the  posterior  or  dor- 
sal commissure,  while  the  latter  forms  the  anterior  or  ventral 
commissure. 

The  cells  of  which  the  walls  of  the  neural  tube  are  composed 
consist  at  first  of  a  single  layer  of  cells  having  a  distinctly  epi- 
thelial character.  They  are  very  long,  extend  in  a  radial  man- 
ner throughout  the  entire  thickness  of  the  walls,  and  lie  very 
close  to  each  other,  thus  having  a  palisade-like  appearance. 
While  the  epithelial  character  of  the  cells  is  preserved,  there 
may  be  distinguished  an  inner  and  an  outer  clear  zone  without 
nuclei,  the  middle  zone  containing  all  the  nuclei,  which  are  in- 
creased in  numbers  as  development  progresses.  Between  the 
inner  clear  zones  of  these  epithelial  cells  and  toward  the  central 
cavity  there  appears  at  the  fourth  or  fifth  week,  in  the  human 
embryo,  a  number  of  cells  spheric  in  shape,  lo  to  14  ^^  in  diam- 
eter, with  nuclei,  which  present  one  or  another  stage  of  karj^o- 
kinesis.  These  are  the  germinating  cells  or  "  Keimzellen  "  of  His. 
They  are  early  transformed  into  neuroblasts,  or  primitive  nerve- 
cells,  by  a  lengthening  out  of  their  cell-body  and  the  formation 
of  a  single  protoplasmic  stalk,  or  axis-cylinder,  which  forms  a 
nerve-fiber.  Along  with  the  growth  of  the  walls  of  the  neural 
tube,  the  epithelial  cells  increase  in  length,  become  vacuolated , 
lose  their  definite  cell-boundary,  and  their  protoplasm  becomes 
filled  with  perforations.  The  individual  cell  appears  as  if  pos- 
sessed of  branching  processes  united  with  those  from  adjacent 
cells,  and  thus  forms  a  network  which  extends  throughout  the 
33 


514 


CENTRAL  NERVOUS  SYSTEM. 


entire  thickness  of  the  embr)'onic  cord.  This  network  has  been 
termed  by  His  myelospongium,  or  neurospongium,  and  the  cells 
from  which  it  is  formed  are  called  spongioblasts,  they  being  the 
primitive  neuroglia  cells.  They  are  at  this  stage  elongated  and 
oblong  in  form,  and  have  oval  nuclei.  Each  spongioblast  pos- 
sesses two  main  processes — an  outer  and  an  inner,  or  peripheral 


Fig.  240. — Fore-part  of  the  Embryo  Viewed  from  the  Dorsal  Side. — {After 
Koelliker,  from   Qttain.) 
F.  Fore-brain,     e.    Ocular  vesicles.     M.    Mid-brain.     H.  Hind-brain,     h.    Part  of  the  heart 
seen  bulging  to  the  right  side.      Voin.  Omphalomesenteric  or  vitelline  veins  entering  the 
heart  posteriorly.     iMr.   Medullary  canal,  spinal  part.    /.   Protovertebral  somites. 


and  central.  The  inner  or  central  processes  course  inward  to 
the  inner  boundary,  where  they  break  up  into  fine  branches, 
vv^hich  unite  to  form  a  close  network  called  the  internal  limiting 
membrane.  The  outer  or  peripheral  processes  branch  and  form 
a  network,  w^hich  is  most  distinct  in  the  outer  layer.  At  a  later 
stage  these  spongioblasts  become  thickened  near  the  position 
of  their  nuclei ;  the  nuclei  proliferate  rapidly  and  then  migrate. 


Fig.  241. — Myelospongium  from   Spinal  Cord  of  Three-and-a-Half-Weeks'  Human 

Embryo. — [His,  from  Quain.) 


Fig.  242. — Inner  Ends  of  Spon- 
gioblasts {sp)  WITH  Germinal 
Cells, ^,  Between  them.  From 
spinal  cord  of  human  embryo. — 
[His,fro7fi  Quain.) 


-Inner  Ends 
OF  Spongioblasts 
{Sp).  A  germinal  cell 
(g)  and  two  transi- 
tional cells  (  7r)  from 
spinal  cord  of  human 
embryo. — [His,  from 
Quain. ) 


Fig.  244. — Three  Neu- 
roblasts, Each  with 
a  Nerve-fiber  Pro- 
cess Growing  out 
Beyond  the  Base- 
ment Membrane  of 
THE  Embryonic  Spi- 
nal Cord.  —  {His, 
from  Quain.) 

515 


EMBRYOLOGY   OF   THE   CENTRAL   NERVOUS   SYSTEM. 


517 


accumulating  about  the  central  canal  and  along  the  periphery 
of  the  medullary  wall  of  the  neural  tube.  Many  of  the  cells 
lose  their  central  processes,  the  outer  process  alone  remaining  ; 
soon  this  process  is  also  lost,  and  lateral  branches  having  devel- 
oped, the  elongated  configuration  of  the  cells  is  lost,  the  cells 
being  transformed  into  the  spheric  neuroglia  or  stellate  cells  of 
Deiter. 

Other  spongioblasts  which  have  accumulated  about  the  cen- 
tral canal  form  for  it  its  epithelial  lining,  or  ependyma.  These 
ependymal  cells  have  fine  radiating  processes  which  pass  through 
the  entire  thickness  of  the  gray  and  white  matter  of  the  embry- 


FiG.  245. — Ependymal  Fiber  of  Marrow  of  a  Seven-days'-old  Embryo  of  a 
Chicken. — {After  Golgi.) 


onic  cord.  About  the  fifth  week  of  embryonic  life  their  free 
surfaces  develop  cilia,  which  extend  into  the  central  cavity. 
These  ependymal  cells  are  identical  in  character  with  neuroglia 
cells.  At  a  period  when  the  neuroblasts,  or  nerve-cells,  can  be 
well  differentiated,  the  medullary  wall  of  the  neural  tube  may 
be  divided  into  three  layers  :  First,  the  outer  neuroglia  layer, 
or  the  Randschleier  of  His,  in  which  location  the  white  matter 
is  developed.  Second,  the  middle  or  mantle  layer,  the  habitat 
for  the  neuroblasts,  or  the  region  of  the  gray  matter.  Third, 
the  inner  layer  of  ependymal  cells. 

The  researches   of  His  have   shown   that  both  the  spongio- 


515 


CENTRAL  NERVOUS  SYSTEM. 


blasts  from  which  the  neuroglia  cells  are  developed  and  the 
neuroblasts  from  which  the  nerve-cells  and  fibers  are  developed 
are  formed  from  cells  of  the  epiblast.  which  are  identical  in 
character.  This  observation  of  His  has  recendy  been  confirmed 
by  Ramon  y  Cajal,  who  states  that  cells  which,  from  their  form 
and  position,  would  be  classed  as  spongioblasts,  frequendy  alter 
their  shape  and,  throwing  out  axis-cylinder  processes,  become 
converted  into  nerve-cells  and  fibers.  The  neuroblasts  of  the 
primitive  nerve-cells  are  pear-shaped,  owing  to  the  development 
from  each  of  an  elongated  protoplasmic  process  which  becomes 
the  axone  of  the  future  nerve-cell.  The  cells  at  this  period  do 
not  possess  dendrites,  they  being  developed  much  later.  The 
neuroblasts  are  capable  of  motion  and  frequendy  alter  their 
position. 

"Fpy 


Fig.  246. — Lower  End  ok  the  Spinal  Cord  of  a  Human  Emp.rvo  of  Three  Months. 

— [From  Minot.) 
Epy.    Ependymal  layer,     n.   Neuroblast  layer.      R.    Outer  neuroglia  layer,  or  Randschleier. 


The  study  of  a  transverse  section  of  the  human  embryonic 
cord  at  the  fourth  w^eek  shows  it  to  be  composed  of  an  outer 
neuroglia  layer,  the  Randschleier,  in  the  meshes  of  which  the 
white  matter  is  developed  ;  of  a  middle  or  mantle  layer,  occu- 
pied by  neuroblasts,  from  which  the  gray  matter  is  developed  ; 
and,  lastly,  an  inner  layer  of  ependymal  cells. 

The  neuroblasts  found  distributed  throughout  the  middle 
layer  tend  to  collect  into  two  large  groups,  which  are  located  in 
the  outer  and  ventral  part  of  this  layer  and  constitute  in  the 
human  embryo  of  six  weeks  the  chief  portion  of  each  half  of 
the  cord.  The  more  ventral  portions  of  these  groups  form  the 
anterior  horns  or  cornua,  the  cells  being  motor  in  funcUon.  The 
axones  of  these  cells  pass,  in  slight  curves,  through  the  ventral 


EMBRYOLOGY   OF   THE   CENTRAL   NERVOUS   SYSTEM. 


519 


portion  of  the  outer  layer,  to  form  the  primitive  anterior  spinal 
nerve-roots.  The  processes  of  the  more  dorsally  located  neuro- 
blasts do  not  leave  the  embryonic  cord,  but  pass  into  the  meshes 
of  the  myelospongium,  where,  according  to  His,  they  meet  re- 
sistance, and  hence  their  direction   is   changed  into  an  upward 


Fig.  247. — Section  of  Spinal  Cord  of  Four 
Weeks'  Human  Embryo. — {Bis,fro}?i  Quain.) 

The  posterior  roots  are  continued  within  the  cord  into 
a  small  longitudinal  bundle  which  is  the  rudiment 
of  the  posterior  white  column.  The  anterior  roots 
are  formed  by  the  convergence  of  the  processes  of 
the  neuroblasts.  The  latter,  along  with  the  elon- 
gated cells  of  the  myelospongium,  compose  the  gray 
matter.  The  external  layer  of  the  cord  is  traversed 
by  radiating  fibers  which  are  the  outer  ends  of  the 
spongioblasts.  The  anterior  commissure  is  begin- 
ning to  appear.  This  figure  is  much  more  magni- 
fied than  the  next  one. 


Fig.  248. — Transverse  Section 
of  the  Cervical  Part  of 
THE  Spinal  Cord  of  a  Human 
Embryo  OF  Six  Weeks. — {After 
KoeUiker,froin  Quain.) 

c.  Central  canal,  e.  Its  epithelial 
lining.  ^^  (superiorly) .  The  orig- 
inal place  of  closure  of  the  canal. 
a.  The  white  substance  of  the  an- 
terior columns.  g.  Gray  sub- 
stance of  anterolateral  horn.  p. 
Posterior  column,  ar.  Anterior 
roots.     /;-.    Posterior  roots. 


and  downward  course.    These  neuroblasts,  with  their  processes, 
form  the  intrinsic  cells  and  fibers  of  the  cord. 

A  cross-section  of  the  cord  at  the  sixth  or  eighth  week  shows 
the  central  canal  elongated  ventrodorsally  and  presenting,  near 
its  middle  on  each  side,  a  lateral  extension  which  cuts  deeply 
into  each  lateral  wall  of  the  medullary  tube,  thus  dividing  the 
primitive  cord   into   the  ventral   and   dorsal  zones  of  His.     At 


520  CENTRAL  NERVOUS  SYSTEM. 

this  Stage  can  be  seen  issuing  from  the  neuroblasts  of  the  ventral 
zones  fibers  proceeding  ventrally  to  reach  the  outside  of  the 
cord  forming  the  anterior  or  motor  nerve-roots.  Entering  the 
dorsal  zones,  fibers  may  be  seen  which  are  the  axones  of  the 
embryonic  posterior  spinal  ganglia.  At  a  later  period  in  devel- 
opment the  central  cavity  decreases  in  size  until  about  the  tenth 
week,  when  its  walls  almost  coalesce  between  the  dorsal  zones, 
leaving  only  a  small  triangular-shaped  opening  in  its  most  dorsal 
extremity.  Still  later  all  traces  of  the  cavity  are  obliterated, 
there  remaining  only  the  central  canal. 

At  the  sixth  week  no  trace  exists  of  the  anterior  and  posterior 
longitudinal  fissures.  The  former  is  due  to  an  arrest  of  devel- 
opment of  the  floor  of  the  central  cavity,  and  a  corresponding 
rapid  development  of  the  ventral  zones  resulting  in  two  bulg- 
ings  which  never  coalesce,  but  become  approximated  in  the 
median  line,  leaving  a  fissure  between  them.  In  this  fissure  is 
found  a  process  of  connective  tissue  from  the  pia.  The  so- 
called  posterior  fissure  is  doubtless  the  remains  of  the  dorsal 
part  of  the  central  cavity,  being  indicated  as  a  mere  slit,  which 
contains  a  process  of  neuroglia  from  the  ependymal  cells  of  its 
dorsal  wall.  This  process  was  named  the  posterior  longitudinal 
fissure  by  early  anatomists,  from  its  resemblance  to  the  anterior 
fissure,  and  the  probability  of  its  containing  a  process  of  pia, 
and,  although  later  anatomists  have  proved  the  falsity  of  this 
view,  it  is  still,  owing  to  long  usage,  convenient  to  retain  the  old 
name,  and  hence  in  the  description  of  the  spinal  cord  it  is  so 
recognized. 

The  anterior  horns  depend,  for  their  growth,  upon  the  con- 
version of  the  germinating  cells  of  the  mantle  layer  into  neuro- 
blasts, and  the  subsequent  growth  of  the  latter  into  complete 
motor  neurones. 

The  cells  of  the  posterior  horns  are  probably  derived  from 
the  dorsal  part  of  the  mande  layer.  The  cervix  of  each  poste- 
rior horn  is  formed  by  the  narrow  part  of  the  gray  matter  con- 
necting the  dorsal  and  ventral  zones  and  located  opposite  the 
central  furrow  or  groove. 

The  white  matter  of  the  cord  is  developed  in  the  outer  layer, 
or  Randschleier  of  His.     This  layer  forms  a  complete  covering 


EMBRYOLOGY   OF  THE   CENTRAL   NERVOUS   SYSTEM. 


521 


for  the  mantle  layer,  or  gray  matter.  In  the  dorsal  zone  on  each 
side  exists  an  oval  projection  of  the  Randschleier,  called  the  oval 
bundle  of  His,  which  extends  from  the  entrance  of  the  most 
ventrally  placed  posterior  root  to  near  the  mid-dorsal  line,  and 
contains  longitudinally  coursing  fibers  from  the  embryonic  pos- 
terior spinal  ganglia.  Increasing  in  size,  each  bundle  extends 
backward  to  the  arch  formed  by  the  union  of  the  dorsal  zones 
with  the  roof  of  the  medullary  tube.  This  arch  gives  rise  to 
the  columns  of  Goll,  which  become  united,  owing  to  the  oblit- 
eration of  the  small  triangular  opening,  this  being  the  remains 


Fig.  249. — Transverse    Section    of    the    Spinal    Cord    from    the    Upper    Dorsal 

Region  of  a  Human  Embryo  of  Six  Weeks.— {/If/e?-  His,  from  Minof.) 

d.pl.    Deck-plate,     ov.b.  Oval  bundle  of  dorsal  zone.      D.R.    Dorsal  root.      Rsch.   Randschleier 

of  ventral  zone.     b.    Floor-plate.     V.  R.   Ventral  root. 


of  the  dorsal  periphery  of  the  central  cavity,  which  lies  between 
them.  The  oval  bundle  continues  to  grow  dorsomesially  and, 
becoming  situated  between  Goll's  columns  and  the  gray  matter, 
unites  with  its  fellow  of  the  opposite  side  to  form  -the  columns 
of  Burdach.  This  oval  bundle  is  connected  with  the  dorsal 
part  of  the  outer  layer,  or  Randschleier,  which  forms  a  covering 
for  the  ventral  zone  by  a  narrow  portion  located  at  the  bottom 
of  a  sulcus,  called  the  central  groove.  This  narrow  portion 
begins  to  grow  rapidly,  and  completely  obliterates  the  central 
groove.     At  this  point  on  each  side  are  developed  the  lateral 


522  CENIRAL  NERVdLS  SYSTEM. 

pyramidal  tracts.  In  that  part  of  the  outer  layer,  or  Randschleier, 
located  between  the  ventral  fissure  and  the  exit  of  the  axones 
of  the  neuroblasts  of  the  ventral  zone  (anterior  horns)  are  formed 
the  anterior  columns  of  the  cord,  while  that  portion  located  be- 
tween the  oval  bundle  and  the  exit  of  the  same  nerve-fibers 
gives  rise  to  the  lateral  columns. 

The  posterior  spinal  ganglia  take  their  origin  from  cells  of 
the  epiblast  located  just  external  to  the  medullary  ridges  of  each 
side,  and  when  these  ridges  meet  at  the  mid-dorsal  line  to  form 
the  neural  tube,  these  groups  of  cells  also  unite  at  the  median 
line  to  form  a  slightly  elevated  portion  of  the  epiblast,  which  is 
termed  the  neural  crest.  At  reo^ular  intervals  aloncr  each  side 
of  this  crest  corresponding  to  the  middle  of  the  mesoblastic 
somites,  or  provertebra,  lateral  projections,  or  outgrowths  of 
cells  appear,  w^hich  separate  from  the  neural  crest  to  form  the 
primitive  posterior  spinal  ganglia. 

The  embryonic  cells  of  the  spinal  ganglia  are  bipolar  in  form, 
each  cell  possessing  both  a  central  and  a  peripheral  axone.  The 
former  enter  the  dorsal  columns  of  the  cord  and  form  the  sen- 
sory nerve-roots,  while  the  latter  have  a  peripheral  course,  and 
are  destined  to  terminate  in  sensory  end  organs.  Toward  the 
end  of  embryonic  life  most  of  these  cells  become  unipolar,  either 
by  fusion  of  their  protoplasmic  processes  or,  what  is  more  prob- 
able, by  an  outgrowth  of  a  protoplasmic  stalk.  This  stalk  or 
pedicle  divides  T-shaped,  one  division  passing  into  the  dorsal 
part  of  the  cord  as  a  posterior  spinal  nerve-root,  where  it  again 
divides  into  a  lono-  ascendino-  and  a  short  descending  branch. 
The  other  process  passes  peripherally  as  a  periphery  sensory 
nerve-fiber  and  terminates  in  a  sensory  end  organ. 

The  fibers  of  the  columns  of  the  cord  have  their  orimn  from 
the  various  parts  of  the  brain,  as  well  as  from  the  spinal  cord 
and  posterior  spinal  ganglia.  They  are  simply  the  lengthened- 
out  axis-cylinder  processes  of  the  cells  of  these  regions  which 
have  grown  in  the  direction  in  which  they  convey  impulses. 
These  fibers  are  at  first  all  non-medullated,  but  receive  their 
myelin  sheaths  at  later  periods  of  development.  Flechsig  has 
shown  that  the  fibers  of  the  different  columns  of  the  cord  re- 
ceive their  myelin  at  certain  definite  periods  of  embryonic  life. 


Fig.  250. — Sections  Across  the  Region  of  the  Calamus  Scriptorius  of  the  Brain. 

—  {His,  from  Qua  in . ) 
A.   Region  of  the  glossopharyngeal  ganglion.     B.   Of  the  auditory  facial  ganglion. 


Fig.  251. — Sections  Across  the  Fourth  Ventricle  of  a  Somewhat   Older 
Embryo. — {His,  from  Qiiain. ) 
A.   Section  taken  through  the  lower  part.     B.   Across  the  widest  part  (trigeminus  region).      C. 
Through  upper  part  (cerebellar  region),     r.   Roof  of  neural  canal,     al.   Alar  lamina,      bl. 
Basal  lamina,     v.   Ventral  border. 


Fig.  252.— Sections  Across  the  Lower  Half  of  the  Fourth  Ventricle  of  a  Still 

Older  Embryo.     Showing  gradual  opening  out  of  the  neural  canal  and  the  commencing 

folding. over  of  the  alar  lamina  (at/). — {His,  from  Qiiain.) 
V.   Ventral  border,     t.  Tenia,      ot.   Otic  vesicle.      ;7.   Recessus  labyrinthi. 
In  the  succeeding  stage  (not  here  represented)  the  angle  at  v  has  almost  disappeared,  the  fold/ 

has  extended  over  the  alar  lamina,  and  the  two  thickened  halves  are  in  the  same  horizontal 

plane,  covered  by  a  greatly  expanded  and  thinned-out  roof. 

523 


EMBRYOLOGY   OF   THE    CENTRAL   NERVOUS   SYSTEM.  525 

SO  that  the  location  and  course  of  the  various  tracts  can  be 
easily  demonstrated. 

The  embryonic  cord  completely  fills  the  cavity  of  the  spinal 
canal  up  to  the  beginning  of  the  fourth  month,  but  at  birth, 
owing  to  a  more  rapid  development  of  the  spinal  canal,  the  lower- 
most part  of  the  cord  (coccygeal  portion)  reaches  only  to  the 
level  of  the  third  lumbar  vertebra,  and  in  the  adult  to  the  lower 
part  of  the  first  lumbar.  This  apparent  ascent  of  the  cord  alters 
the  course  of  the  nerve-roots  running  out  of  it.  At  first  these 
roots  leave  the  cord  nearly  at  right  angles,  but  later,  owing  to 
the  before-described  changes,  these  fibers  have  an  oblique  or 
a  nearly  longitudinal  course  within  the  spinal  canal.  In  the 
lumbar  and  sacral  parts  of  the  cord  these  descending  fibers  form 
the  Cauda  equina.  The  cervical  and  lumbar  enlargements  are 
well  differentiated  at  the  fourth  month  of  fetal  life. 

The  membranes  and  the  blood-vessels  of  the  cord  are  both 
derived  from  the  mesoblast,  which  has  formed  a  canal  around 
the  neural  tube. 


DEVELOPMENT  OF  THE  MEDULLA  OBLONGATA. 

The  medulla  oblongata  is  developed  from  the  fifth  or  after- 
brain  vesicle — the  metencephalon.  Although  the  medulla  differs 
in  shape  from  the  spinal  cord,  its  development  is  essentially  the 
same.  Early  in  the  growth  of  the  after-brain  vesicle  there  is  to 
be  distinguished  a  floor  (Bodenplatte),  lateral  walls,  and  a  roof 
(Deckplatte).  From  thickenings  of  the  floor  and  lateral  walls 
are  developed  (third  month)  the  anterior  and  lateral  columns, 
continuous  with  those  of  the  cord.  From  the  roof  no  nerve- 
cells  are  developed,  and  it  retains  its  epithelial  character  and 
becomes  spread  out  over  quite  an  extensive  surface,  forming  a 
covering  to  the  cavity  of  the  metencephalon,  or  fourth  ventricle. 
Later,  this  covering  becomes  blended  with  the  under  surface  of 
the  pia,  which  is  very  vascular,  the  vessels  being  arranged  into 
two  rows  of  villous  processes  which  grow  into  the  cavity  of  the 
after-brain  vesicle,  to  form  the  choroid  plexuses  of  the  fourth 
ventricle,  or  tela  choroidea  inferior. 

Transverse  section   of  the   metencephalon  in   an   embryo  of 


526 


CENTRAL   NERVOUS  SYSTEM. 


about  three  weeks  shows  the  primitive  medulla  to  be  more  or 
less  shield- shaped,  with  a  triangular  medullary  cavity.  This 
appearance  is  due  to  the  growth  laterally  of  the  thin  dorsal  wall 
or  roof  which  forms  the  base,  while  the  dorsal  halves  of  the 
lateral  walls  are  spread  widely  apart ;  their  ventral  halves,  which 
meet  the  dorsal  at  a  distinct  angle,  gradually  converge  and  join 
the  floor  of  the  meduUarv  wall  in  the  median  line.  The  anofle 
of  junction  of  the  dorsal  and  ventral  parts  of  each  lateral  wall 
serves  to  separate  the  medullary  walls  into  the  dorsal  and  ventral 
zones  of  His.  Owing  to  the  widening  of  the  medullary  tube 
and  the  expansion  of  the  roof,  the  dorsal  and  ventral  zones  are 
brought  nearly  into  one  plane.  Along  the  edge  of  the  dorsal 
zone  a  fold,  bv  which  the  edq-e  is  arched  outward  and  downward, 


RL 


Fig.  253. — Transverse  Section   of  the  Medulla  Oblong.^ta   of   His'    Embryo   Ru 

(Length  of  Back,  9.1  mm.). — {After  IV.  His,  from  Minot.) 

RL.   Rhomboid  lip.     Ts.  Tractus  solitarius.     X.  Vagus  nerve.     XIL   Hypoglossal  nerve. 

is  formed  and  is  separated  from  the  dorsal  zone  by  an  external 
notch.  This  fold  has  been  called  the  fold  of  the  rhomboid 
fossa — the  Rautenlippe. 

The  walls  of  the  metencephalon,  as  well  as  those  of  the  rest 
of  the  cerebral  vesicles,  may  be  early  differentiated,  owing  to  an 
orderly  arrangement  of  the  spongio-  and  neuroblasts,  into  three 
distinct  layers — an  outer  neuroglia  or  white  matter  (the  Rand- 
schleier),  the  middle  mantle  or  gray  matter,  and  the  inner  or 
ependymal  layer. 

The  lower  boundary  of  the  dorsal  zones  is  indicated  by  an 
oval-shaped  area  on  each  side  containing  longitudinal  nerve- 
fibers,  axones,  and  collaterals  from  the  cerebral  ganglia  :  these 
are  the  solitarv  bundles  or  tracts.     Thev  are  homoloofous  with 


EMBRYOLOGY   OF  THE   CENTRAL   NERVOUS   SYSTEM. 


527 


the  oval  bundles  of  the  Randschleier  of  the  spinal  cord.  The 
ventral  zones  are  separated  from  each  other  above  by  a  median 
groove,  which  begins  at  a  point  where  the  central  canal  widens 
and  extends  to  the  aqueduct  of  Sylvius.  On  each  side  of  this 
groove  is  developed  an  eminence  which  later  is  called  the 
eminentia  teres.  The  ventral  zones  are  separated  laterally 
from  the  dorsal  by  a  less  prominent  groove,  the  remains  of  which 
are  indicated  in  the  adult  by  the  fovea  anterior  and  posterior. 
The  fold,  or  Rautenlippe,  on  each  side  grows  downward  and 
unites  with  the  main  fold  of  the  dorsal  zone  ;  by  so  doing  it 
surrounds  the  solitary  bundle,  displacing  it  inward,  so  that  it 
comes  to  occupy  a   deeper  position.     At  this  stage  the  dorsal 


Fig.  254. — -Transverse  Section  of  the  Medulla  Oblongata  of  His'  Embryo  Mr. 
— [After  W.  His,  from  Minot.) 
T.   Tractus  solitarius.      RL.    Secondary  rhomboid  lip.     F.r.   Funiculus  restiformis.      a.Tr.   As- 
cending trigeminal  tract. 


and  ventral  zones  are  in  about  the  same  plane,  the  groove  sepa- 
rating them  being-  nearlv  obliterated.  In  the  dorsal  zone  are 
developed  the  restiform  body,  the  clava,  the  solitary  bundle,  and 
the  descendino-  trig-eminal  nucleus  and  tract.  The  nucleus  of 
Burdach's  column  is  probably  derived  from  the  Rautenlippe. 

The  neuroblasts  of  the  dorsal  zone  that  are  developed  during 
the  fourth  week  form  the  arcuate  fibers.  The  neuroblasts  of 
this  zone  which  are  formed  later  migrate  in  tracts,  both  within 
and  outside  of  the  solitary  bundle,  into  the  lower  part  of  the 
ventral  zone,  where,  with  other  neuroblasts,  they  form  the  oHvary 
body. 

The  raphe,  which  is   a  neuroglia  partition  between  the  ven- 


52S  CENTRAL   NERVOL'S  SVSrEM. 

tral  zones,  arises  from  a  thickening  of  the  floor  of  the  medullary 
wall.  It  is  the  place  of  crossing  of  fibers  from  one  side  of  the 
medulla  to  the  opposite  ;  no  neuroblasts  can  migrate  across  this 
partition. 

The  neuroblasts  of  the  gray  matter  (mantle  layer)  of  the 
ventral  zone  enter  chiefly  into  the  production  of  the  formatio 
reticularis  ;  those  that  have  miofrated  from  the  dorsal  zone  form 
the  main  and  accessory  olivary  bodies.  The  layer  of  neuro- 
blasts beneath  the  ependyma  gives  rise  to  the  motor  cranial  nuclei 
in  this  region.  In  the  outer  layer  (neuroglia),  or  Randschleier, 
are  developed  the  white  columns  of  the  medulla.  This  outer 
layer  is  divided  by  the  exits  of  the  ventral  nerve-roots  (hypo- 
glossal) into  a  median  or  ventral  and  lateral  regions  corre- 
sponding to  the  anterior  and  lateral  columns  of  the  cord.  In 
the  dorsal  part  of  the  median  region  are  developed  longitudinal 
fibers  which  collect  into  bundles  and  form  the  posterior  longi- 
tudinal bundles.  At  the  fourth  month  large  numbers  of  longi- 
tudinal fibers  appear  in  the  ventral  parts  of  the  median  region  ; 
these  fibers  form  the  anterior  pyramids.  The  lateral  region  of 
each  side  contains  the  fibers  of  the  restiform  body,  some  arcuate 
fibers,  descending  trigeminal  nerve-fibers,  solitary  bundle,  and 
nucleus  of  Burdach's  columns. 


CEREBELLUM  AND  PONS. 

The  cerebellum  and  pons  Varolii  are  developed  from  the 
fourth  cerebral  vesicle,  or  epencephalon.  This  vesicle  is  con- 
tinuous behind  with  the  metencephalon,  or  fifth  vesicle,  the  two 
together  forming  the  elongated,  somewhat  boat-shaped  cavity — 
the  embryonic  fourth  ventricle.  The  epencephalon  is  separated 
from  the  metencephalon,  or  mid-brain,  by  a  narrow  constricted 
part  of  the  neural  tube,  called  by  His  the  isthmus.  The  cere- 
bellum grows  out  from  the  dorsal  wall  or  roof  of  the  fourth 
cerebral  vesicle,  and  becomes  located  between  the  medulla 
oblonorata  and  the  isthmus.  From  the  floor  of  this  vesicle  the 
pons  Varolii  becomes  developed.  As  early  as  the  third  month 
the  transverse  fibers  so  characteristic  of  the  pons  may  be  dis- 
tinguished.    The  growth  of  the  pons  is  very  rapid,  and  proceeds 


EMBRYOLOGY    OF   THE    CENTRAL    NERVOUS   SYSTEM. 


529 


pari  pas siL  with  that  of  the  cerebellum.  The  lateral  walls  give 
rise  to  the  middle  cerebellar  peduncles.  The  cerebellum 
appears  at  first  as  a  budding  forward  of  the  dorsal  wall  of  the 
epencephalon,  which,  as  it  grows,  forms  a  distinct  transverse 
thickening  or  ridge  overhanging  the  thin  roof  of  the  medulla 
oblongata.  At  about  the  third  month  of  embryonic  life  the 
middle   portion  of   this    ridge    increases   in   size,   and  becomes 


Fig.  255. — Median  Section  through  the  Brain  of  a  Two  and  a  Half  Months' 
Fetus. — ^His,  frofn  Quain. ) 

The  mesial  surface  of  the  left  cerebral  hemisphere  is  seen  in  the  upper  and  right-hand  part  of 
the  figure ;  the  large  cavity  of  the  third  ventricle  is  bounded  above  and  in  front  by  a  thin 
lamina  ;  below  is  seen  the  infundibulum  and  pituitary  body.  Filling  the  upper  part  of  the 
cavity  is  the  thalamus  opticus ;  in  front  and  below  this  is  the  slit-like  foramen  of  Monro. 
Behind  the  thalamus  is  seen  another  slit-like  opening  which  leads  into  the  still  hollow  ex- 
ternal geniculate  body. 

olf.  Olfactory  lobe.  /.  Pituitary  body.  c.q.  Corpora  quadrigemina.  cb.  Cerebellum,  m.o. 
Medulla  oblongata. 


differentiated  from  the  lateral  parts  by  the  development  of  four 
rather  deep  transverse  grooves  or  fissures,  which  serve  to  divide 
it  into  three  permanent  lobes.  The  middle  portion,  or  lobe  is 
called  the  worm,  or  vermis.  From  now  on  the  lateral  parts 
increase  greatly  in  size,  growing  outward  on  each  side  to  form 
the  cerebellar  hemispheres,  right  and  left.  The  cerebellum,  or 
expanded  roof  of  the  fourth  cerebral  vesicle,  is  connected  in 
front  with  that  of  the  mid-brain,  and  behind  with  the  choroid 
34 


530  CENTRAL  NERVOUS  SYSTEM. 

plexus  of  the  after-brain  vesicle,  or  fourth  ventricle,  by  two 
lamellae  of  white  matter — the  anterior  and  posterior  or  superior 
and  inferior  medullary  velum  (Figs.  255  and  256). 


CORPORA  QUADRIGEMINA,   CRURA  CEREBRI,   AND 
AQUEDUCT  OF  SYLVIUS. 

THE    THIRD    CEREBRAL    VESICLE    (SECOND    PRIMITIVE  VESICLE), 
MESENCEPHALON,    OR    MID-BRAIN. 

This  part  of  the  embryonic  neural  tube  develops  very  rapidly, 
and,  in  consequence  of  the  cephalic  curvatures  of  the  medullary 
tube,  it  at  first  occupies  the  summit  of  the  brain  vesicles.  In 
front  it  is  continuous  with  the  fore-brain,  and  behind  with  the 
hind-brain.  Owing  to  the  much  more  rapid  development  of  the 
hemispheric  vesicles,  together  with  th^t  of  the  cerebellum,  the 
mid-brain  is  completely  covered  in.  In  man  only  a  small  part 
of  the  brain  is  developed  from  this  vesicle.  Its  walls  become 
uniformly  thickened,  thus  narrowing  the  cavity  into  a  small  per- 
manent canal,  which  communicates  above  with  the  third  ven- 
tricle, or  ventricle  of  the  inter-brain,  and  below  with  the  fourth 
ventricle,  or  ventricle  of  the  hind-brain.  This  narrowed  canal 
is  called  the  aqueduct  of  Sylvius.  From  the  thickened  anterior 
w^all  (floor)  the  peduncles  of  the  cerebrum  (crura  cerebri)  are 
developed  ;  these  appear  at  the  third  month  as  two  rounded, 
longitudinal  ridges  on  each  side  of  the  median  line.  It  is  prob- 
able that  a  large  part  of  the  posterior  perforated  space  is  also 
developed  from  this  same  area,  and  appears  in  the  adult  as  a 
triangular  gray  lamina  between  the  crura  cerebri.  The  dorsal 
region  or  roof  of  the  mid-brain  becomes  much  thickened,  and  is 
divided  at  the  third  month  into  two  lateral  halves  by  the  develop- 
ment of  a  median  groove,  and  these  halves  are  again  separated 
at  the  fifth  month  by  the  appearance  of  a  transverse  groove, 
into  four  parts,  two  ventral  and  two  dorsal  ;  these  are  the 
corpora  quadrigemina. 


EMBRYOLOGY  OF  THE  CENTRAL  NERVOUS  SYSTEM. 


531 


OPTIC  THALAMI,  INFUNDIBULUM,  PITUITARY  BODY, 
PINEAL  GLAND,  CORPORA  MAMMILLARIA,  AND 
OPTIC    CHIASM. 

The  first  primitive  cerebral  vesicle,  or  fore-brain,  owing  to  the 
development  by  a  process  of  budding-  out  of  its  ventral  wall  of 
a  secondary  vesicle  whose  growth  is  exceedingly  rapid,  becomes 
located  between   this  fully  developed  secondary  fore-brain,  or 


Fig.  256.^Fetal  Bkain  of  the  Third  Month — {His,fro>n  Qiiain.) 
The  brain  is  represented  in  profile,  but  the  external  wall  of  the  right  hemisphere  has  been  re- 
moved to  show  the  interior  of  the  lateral  ventricle  with  the  corpus  striatum  curving  around 
the  bend  of  the  fossa  of  Sylvius.  The  curved  projections  above  the  corpus  striatum  are 
infoldings  of  the  mesial  wall  of  the  hemisphere  vesicle.  The  lettering  is  the  same  as  in 
figure  255. 

prosencephalon,  and  the  mid-brain  ;  hence  its  name,  dienceph- 
alon,  inter-brain  or  between-brain.  The  inter-brain  at  the  fifth 
week  is  oblong  in  shape,  distinctly  narrowed  at  its  anterior 
extremity  where  it  joins  the  cerebral  hemispheres,  less  so  at  its 
posterior  extremity,  which  is  attached  to  the  mid-brain.  From 
its  walls  grow  out  on  each  side  at  a  very  early  period  two  hollow 
protrusions,  the  primary  optic  vesicles,  the  details  of  which  will 
be  considered  later.  Its  cavity  (third  ventricle)  communicates 
with  the  cavities  of  the  cerebral  hemispheres  (lateral  ventricles) 


532  CENTRAL  NERVOUS  SYSTEM. 

by  an  opening  on  each  side  which  at  first  is  very  large,  Ijut  later 
becomes  exceedingly  narrowed,  owing  to  the  growth  ot  the 
cerebral  hemispheres.  These  openings  of  communication  are 
termed  the  foramina  of  Monro.  Posteriorly,  the  cavity  com- 
municates with  the  cavity  of  the  hind-brain  (fourth  ventricle)  by 
means  of  the  central  canal  of  the  mid-brain  (aqueduct  of 
Sylvius). 

Each  optic  thalamus  is  formed  by  a  marked  thickening  of 
the  lateral  walls,  which  grow  gradually  inward  into  the  cavity  of 
the  inter-brain,  converting  it  into  a  narrow  cleft,  which  is  perma- 
nent, and  located  between  the  convex  surfaces  of  the  optic 
thalami.  This  cleft  is  called  the  third  ventricle.  The  inner 
convex  surfaces  of  the  optic  thalami  meet  across  the  middle  of 
this  space,  their  union  forming  the  middle  or  soft  commissure. 

At  the  beeinninof  of  the  fourth  week  the  floor  of  the  inter- 
brain  cavity  is  prolonged  downward,  forming  a  funnel-shaped 
diverticulum,  which  remains  throughout  life,  and  is  called  the 
infundibulum.  Connected  with  the  apex  of  the  infundibulum 
is  the  pituitary  body,  or  hypophysis  cerebri.  The  roof  of  this 
cavity  resembles  that  of  the  hind-brain,  from  the  fact  that  it  per- 
sists as  a  simple  epithelial  layer  which  unites  with  the  under 
surface  of  the  pia  mater,  the  two  together  forming  a  fold  which 
is  deflected  into  the  cavity,  and  from  which  are  suspended  the 
choroid  plexus  (tela  choroidea  superior)  of  the  third  ventricle. 

In  connection  with  the  growth  of  the  inter-brain  mention 
must  be  made  of  the  evolution  of  two  as  yet  functionally  un- 
known parts — the  pineal  gland,  or  epiphysis  cerebri,  and  the 
pituitary  body,  or  hypophysis  cerebri.  The  former  takes  its 
oriorin  from  the  roof;  the  latter  from  the  floor  of  the  inter-brain. 

The  pineal  gland  develops  in  man  at  about  the  sixth  week 
as  a  median  dorsal  budding  or  outgrowth  from  the  roof  of  the 
inter-brain  at  a  point  where  it  becomes  continuous  with  the 
roof  of  the  mid-brain.  It  has  at  first  a  tubular  shape  resem- 
bling somewhat  the  finger  of  a  glove.  In  all  vertebrates  except 
man  it  is  directed  forward  in  its  growth,  and  is  retained  in  that 
position,  but  in  man  it  develops  in  an  opposite  direction,  coming 
to  lie  on  the  mid-brain  roof. 

It   terminates  blind,  but   its  cavity  is  at  first  continuous  with 


A 


/t  ?i 


St  — 


^\ 


\ 


Fig.  257. — Transverse  Sections  through  the  Brain  of  a  Sheep's  Embryo  of  2.7 
CM.  in  Length. — {After  Koelliker,f7-om  Quaiti.) 

In  A,  the  section  passes  through  the  foramina  of  Monro  ;  in  B,  through  the  third  and  lateral  ven- 
tricles somewhat  further  back.  st.  Corpus  striatum,  ih.  Optic  thalamus,  t.  Third  ven- 
tricle, c,  c' .  Rudiment  of  internal  capsule  and  corona  radiata.  /.  Lateral  ventricle  with 
choroid  plexus,  //.  h.  Hippocampus  major.  /.  Primitive  falx.  a.  Orbitosphenoid.  sa. 
Presphenoid.  /.  Pharynx,  ch.  Chiasma.  0.  Optic  nerve,  m,  m.  Foramina  of  Monro. 
to.   Optic  tract,      ink.   Meckel's  cartilage. 

533 


EMBRYOLOGY   OF   THE   CENTRAL   NERVOUS   SYSTEM.  535 

that  of  the  third  ventricle.  Later  in  its  development,  budding 
processes  appear  from  thickenings  of  its  walls,  which  divide  the 
cavity  of  the  gland  into  a  number  of  compartments  or  folHcles 
which  are  lined  with  cylindric  ciliated  epithelium.  In  man  the 
follicles  tend  to  become  solid  and  contain  deposits  of  calcareous 
matter.  In  the  roof  of  the  inter-brain,  just  dorsal  to  the  pineal 
gland,  fibers  appear  having  a  transverse  course,  connecting 
the  posterior  parts  of  the  optic  thalami.  They  form  the 
posterior  commissure.  In  reptiles,  according  to  Spencer,  the 
pineal  gland  remains  as  a  long  stalk  whose  distal  or  periph- 
eral end  lies  beneath  the  epidermis,  having  passed  through  an 


F16.  258. — Brain  of  a  Chick  Embryo,  Fourth  Day. — [After  Duval,  from  Afifiot.) 

I.   First,  II,  second,  cerebral  vesicle.    Ep.   Epiphysis  or  pineal  gland.    H.    Cerebral  hemisphere. 

L.   Lens,  surrounded  by  the  optic  vesicle,     ot.   Otocyst.     Md.   Hind-brain. 

opening  In  the  roof  of  the  skull  (parietal  bone),  called  the 
parietal  foramen.  This  portion  of  the  sac  enlarges  into  a  hol- 
low globe,  which  soon  becomes  flattened.  The  wall  next  to  the 
epidermis  thickens  to  form  a  lens-like  structure,  while  the  oppo- 
site part  of  the  wall  to  which  the  stalk,  is  attached  has  a  retina- 
like construction. 

In  the  region  of  the  retina  nucleated  cells,  together  with  pig- 
ment, have  been  observed,  and  in  the  stalk,  nerve-fibers  are 
found.  The  development  of  this  body  in  reptiles,  the  forma- 
tion of  a  lens-  and  retina-like  structure,  together  with  the  pres- 
ence of  cells  and   pigment   in   the   latter,  and   the   presence  of 


536  CENTRAL  NERVOUS  SYSTEM. 

nerve-cells  in  the  stalk,  all  indicate  that  it  must  be  a  true  but 
rudimentary  eye. 

The  pituitary  body,  or  hypophysis  cerebri,  has  a  double 
origin  from  the  epiblast,  it  being  developed  in  part  from  the 
oral  cleft  and  in  part  from  the  floor  of  the  inter-brain.  In  man 
at  the  sixth  week  there  is  developed  from  the  oral  cleft  a  hollow 
protrusion  upward  and  backward  toward  the  inter-brain.  This 
protrusion  is  called  the  pouch  of  Rathke,  or  the  pocket  of  the 
hypophysis.  This  pouch  becomes  constricted  at  its  origin,  but  re- 
mains connected  for  a  long  time  with  the  oral  cavity  by  a  narrow 
canal  or  duct,  which  eventually  becomes  obliterated.  At  about 
the  same  time  a  somewhat  similar  protrusion  forms  from  the 
floor  of  the  inter-brain  (infundibulum),  which  enlarges  downward 
and  backward  toward  the  hypophysis,  the  end  of  which  subse- 
quently becomes  fused  with  the  posterior  wall  of  the  hypoph- 
ysis, there  being  no  communication  between  either  cavity. 
The  sac  of  the  hypophysis  toward  the  end  of  the  second  month 
(His)  develops  a  number  of  projecting  processes  or  buds  which 
increase  in  size  and  branch,  and  have  developed  between  them 
numerous  blood-vessels.  Ultimately,  these  processes  become 
separated  from  the  parent  sac  and,  continuing  to  grow,  form 
with  that  sac  a  distinct  lobe,  to  the  posterior  wall  of  which  is 
applied  the  end  of  the  infundibulum,  the  latter  resting  in  a 
slight  depression  between  two  lateral  thickenings  of  the  Lobe. 
The  ventral  portion  of  the  pituitary  body  is  termed  the  glandu- 
lar portion,  while  the  dorsal  part  is  called  the  infundibular  por- 
tion. In  both  divisions  of  the  gland  nerve-fibers  exist,  but  in 
the  glandular  portion  they  belong  only  to  the  sympathetic  sys- 
tem. F"rom  the  floor  of  the  inter-brain  are  developed,  in  addi- 
tion to  the  infundibulum,  the  corpora  mammillaria,  tuber 
cinereum,  ventral  part  of  the  posterior  perforated  space,  and 
the  optic  chiasm. 

The  corpora  mammillaria,  or  albicantia,  appear  at  first  as 
a  roundish  elevation  of  the  floor  in  the  median  line,  which  later 
become  divided  by  a  median  depression  into  two  permanent 
tubercles.  The  small,  elevated  portion  of  the  floor  which  slopes 
toward  the  infundibulum  is  known  as  the  tuber  cinereum.  Its 
development  is  but  imperfectly  understood. 


tJR] 


h.m. 


Fig.  259.— Three  Sections  through  the  Fore-brain  of  a  Four  and  a  Half 

Weeks'   Embryo. — [^His,from  Qiiain.) 
Through  the  lower  anterior  part  of  the  fore-brain.      S.  Falx.     Sf.   Fold  of  roof  passing  below 
falx    toward    the    third  ventricle.     Bf.   Fold  forming  the  sulcus  ammonis.     v.RL,  h.Rl. 
Anterior  and  posterior  parts  of  olfactory  lobe.      Cs.   Corpus  striatum.      O.  W.   Groove  con- 
tinuous with  optic  stalk.      P.s.   Pars  subthalamica.      T.c.   Tuber  cinereum. 
Section  a  little  further  back.     Sf\%  replaced  by  a  less  prominent  but  broader  fold  of  the  roof, 
Ad,  which  subsequently  receives  the  choroid  vessels,  and  is,  therefore,  the  choroid  fold. 
Hs.  Hemisphere  vesicle.      Th.   Thalamus.     S.RI.  Sulcus  of  Monro,  below  and  behind  the 
thalamus. 
C.   Still  further  back.     Ad.   Choroid  fold  here  projecting  into  lateral  ventricles,  but  still  free  from 
mesoblast  and  blood-vessels.     Ma.   Mammillary  tubercle.      The  other  lettering  as  before. 

537 


A 


B 


EMBRYOLOGY   OF   THE   CENTRAL   NERVOUS   SYSTEM.  539 

The  Optic  Chiasm. — From  the  ventral  part  of  the  floor  of 
the  inter-brain  there  is  formed  a  transverse  ridge-hke  thickening 
through  which  later  the  fibers  of  the  optic  nerves  pass  ;  this  is 
primitive  optic  chiasm. 


DEVELOPMENT    OF    THE    CEREBRAL    HEMISPHERES.- 

The  secondary  fore-brain,  or  prosencephalon,  develops  at  first 
as  a  single  vesicle  from  the  ventral  wall  of  the  primary  fore- 
brain.  This  vesicle  soon  enlarges  forward  and  upward  and 
becomes  divided  by  an  infolding  of  the  medullary  wall  in  the 
median  line  in  front,  and  above  into  two  hemispheral  vesicles, 
right  and  left.  The  groove  produced  as  a  result  of  the  deep 
infolding  of  the  medullary  wall  carries  a  process  of  connective 
tissue  from  the  mesoblast,  which  becomes  the  falx  cerebri,  and 
the  groove  is  called  the  longitudinal  fissure.  The  median  walls 
of  each  hemisphere  come  close  together,  being  only  separated 
by  the  falx  cerebri  lodged  in  the  longitudinal  groove ;  owing  to 
this  fact  the  median  surfaces  become  flattened.  Just  in  front  of 
the  ventral  wall  (lamina  terminalis  of  His)  of  the  cavity  of  the 
inter-brain  (third  ventricle),  the  median  walls  of  the  hemispheres 
are  not  separated  by  the  falx  cerebri,  but  form  a  solid  septum 
somewhat  triangular  in  shape,  continuous  behind  with  the  lamina 
terminalis,  in  front  with  the  corpus  callosum,  and  below  with  the 
corpora  striata.  Within  this  septum  in  man  is  found  a  closed 
cavity  which  does  not  communicate  with  the  general  ventricular 
cavities  ;  it  is  termed  the  fifth  ventricle.  The  walls  of  the  hemi- 
spheral vesicles  are  at  first  very  thin,  each  inclosing  a  very  large 
cavity — the  lateral  ventricle.  The  lateral  ventricles  communicate 
with  the  cavity  of  the  inter-brain  (third  ventricle)  by  very  large 
openings  on  each  side — the  foramina  of  Monro.  These  foramina 
gradually  decrease  in  size,  owing  to  an  increase  in  growth  of 
their  walls,  until  they  are  converted  into  mere  slit-like  openings. 

In  connection  with  the  study  of  the  further  development  of 
the  cerebral  hemispheres  must  be  considered,  first,  its  extraor- 
dinary growth  ;  second,  the  infolding  of  its  thin  walls  to  form  a 
few  deep  primary  fissures  with  corresponding  projections  into 
the  ventricular  cavities  ;  third,  the  development  of  the  commis- 


540 


CENTRAL  NERViJUS  SVSTKM. 


sures  throug-h  which  each  hemisphere  is  brought  into  functional 
relation  with  the  other  ;  fourth,  the  development  of  numerous 
other  infoldings  or  hssures  varying  in  depth,  but  without  corre- 
sponding internal  projections. 

The  hemispheral  vesicles  grow  very  rapidly  at  first,  forward, 
upward  and  outward,  and  then  backward,  so  that  at  the  third 
month  they  cover  the  region  of  the  inter-brain  (optic  thalami), 
at  the  end  of  the  fourth  month  they  reach  the  mid-brain  (corpora 
quadrigemina),  and  at  the  beginning  of  the  sixth  month  they 
have    completely  covered  the    corpora    quadrigemina   and  the 


Fig    260. — The  Surface  of  the  Fetal  Brain  at  Six  Months. — {R.  Wagner,  from 

Qua  1)1.) 
This  figure  shows  the  formation  of  the  principal  fissures.     A.   From  above.     B.   From  the  left 
side.      /".   Frontal  lobe.      F.   Parietal.      O.   Occipital.       T.   Temporal.      a,  a,  a.   Slight 
appearance  of  sulci    in    the   frontal  lobe.     s.  Sylvian    fissure,     s' .   Its   anterior   division. 
Within  it,  C,  the  central  lobe.     r.    Rolandic  sulcus.     /.    Parieto-occipital  fissure. 


greater  part  of  the  cerebellum,  beyond  which  they  project  at 
the  seventh  month.      (See  Figs.  257,  259.  and  260.) 

The  Fossa  or  Fissure  of  Sylvius. — This  is  the  first  pri- 
mary sulcus  to  appear.  It  may  be  recognized  as  early  as  the 
fifth  week  of  fetal  life.  It  is  at  first  discernible  as  a  broad, 
shallow  depression,  which  becomes  gradually  deeper,  being  due 
to  an  infolding  of  the  convex  walls  of  the  hemispheral  vesicle 
at  the  middle  of  its  lower  margin.  The  inner  part  of  the  wall 
of  the  depression  becomes  very  much  thickened,  and  forms  an 
elevation  which  extends  alone  the  whole  length  of  the  floor  of 


EMBRYOLOGY   OF   THE   CENTRAL   NERVOUS   SYSTEM.  541 

the  hemisphere,  and  projects  into  the  cavity  of  the  lateral 
ventricle.  This  is  the  primitive  corpus  striatum,  and  the 
thickening  of  which  it  is  a  part  is  continuous  posteriorly  with 
that  part  of  the  inter-brain  which  forms  the  optic  thalamus. 
(See  Fig.  257.)  A  part  of  this  thickening  on  each  side  con- 
tinuous with  the  outer  part  of  the  optic  thalamus  assists  in  the 
formation  of  the  cerebral  peduncles.  The  outer  part  of  the 
hemispheral  wall,  which  forms  the  floor  of  the  fossa  of  Sylvius, 
afterward  becomes  the  insula,  or  island  of  Reil,  which  at  the 
ninth  month  is  converted  into  a  number  of  small  gyri  (gyri 
breves  insula)  by  the  formation  of  several  small  sulci.     i\t  the 


pm 


Fig.  261. — Brain  of  a  Human  Emhryo  of  about  Three  Months  (According  to 
Marchand,  Four  Months). — {^After  F.  Mar chand,  from  Miiiot.) 
th.  Optic   thalamus,     bf.   Bogenfurche.      c.c.   Corpus    callosum.      Sp.   Septum   lucidum.     c.a. 
Anterior   commissure.       OI.   Olfactory  lobe.       Chi.   Optic  chiasma.       inf.   Infundibulum. 
Pons.   Pons  Varolii,     cbl.  Cerebellum,      mb.    Mid-brain,     pin.   Pineal  gland. 


fifth  month  the  fossa  of  Sylvius  becomes  much  deeper,  of  greater 
length,  and  has  an  oblique  direction.  The  margins  of  the  fossa, 
increasing  in  size,  approach  each  other  and  completely  conceal 
from  view  the  island  of  Reil,  forming  for  it  an  operculum,  thus 
converting  the  fossa  into  the  fissure  of  Sylvius,  The  anterior 
limb  of  the  fissure  is  formed  by  an  infolding  of  the  wall  just  in 
front  of  the  fossa  of  Sylvius,  Owing  to  the  formation  of  the  fossa 
of  Sylvius  each  hemisphere  is  divided  into  two  primary  lobes, 
one  ventral,  the  other  dorsal,  to  the  fossa.  The  ventral  one  is 
called  the  frontal  lobe,  while  the  dorsal  receives  the  name  of  the 


542  CENTRAL  NERVOUS  SYSTEM. 

temporal  lobe.  A  part  of  this  latter  lobe  dev^elops  backward 
toward  the  cerebellum  and  forms  the  occipital  lobe  (Fig.  260). 

The  lateral  ventricles,  because  of  the  before-mentioned 
changes,  are  much  reduced  in  size,  and  conform  more  or  less 
to  the  shape  of  the  hemisphere,  being  somewhat  arched  or 
ring-like  in  shape.  That  part  of  the  lateral  ventricle  remaining 
in  the  frontal  lobe  is  termed  the  anterior  cornu,  the  portion 
which  descends  into  the  temporal  lobe  is  called  the  middle  or 
descending  cornu,  while  the  part  which  extends  backward  and 
inward  into  the  occipital  lobes  is  the  posterior  cornu. 

Along  the  median  line  of  the  hemisphere  is  developed  a  fold 
which  produces  an  external  groove  and  a  corresponding  internal 
ridge.  This  groove  is  the  primary  fissure,  or  Bogenfurche 
of  His.  It  begins  in  front  at  the  olfactory  lobe,  which  it  divides 
into  an  anterior  and  a  posterior  part,  and  continuing  backward 
in  a  curved  direction  joins  a  corresponding  groove,  the  hippo- 
campal  sulcus,  which  is  also  the  result  of  an  infolding  of  the 
median  wall  of  the  temporal  lobe.  There  is  thus  formed  a  long, 
arched  fissure  ;  hence  its  name,  arcuate  fissure,  "  Boofenfurche." 
The  posterior  end  of  this  groove  or  fissure  branches  and  forms 
the  internal  parieto-occipital  and  calcarine  fissures.  This  pri- 
mary fissure  and  the  fissure  of  Sylvius  are  the  only  ones  formed 
by  an  infolding  of  the  hemisphere  walls,  all  others  being 
simple  depressions  of  these  walls.  The  internal  ridge  corre- 
sponding to  the  primary  fissure  or  groove  has  the  same  arched 
course.  The  posterior  half  of  the  ridge  forms  the  hippocampus 
major,  or  cornu  ammonis,  and  that  part  of  the  ridge  which 
corresponds  to  the  branch  known  as  the  calcarine  fissure 
develops  the  hippocampus  minor,  or  calcar  avis.  Nothing  is 
known  of  the  further  development  of  the  anterior  half  of  this 
ridge.  The  narrow  portion  of  the  hemisphere  wall  located  just 
below  this  ridge  is  called  the  Randbogen,  or  gyrus  arcuatus,  a 
large  part  of  which  is  occupied  by  the  corpus  callosum.  The 
part  of  the  Randbogen  just  dorsal  to  the  corpus  callosum  is 
beset  with  a  number  of  small,  transverse  ridores,  and  forms  the 
dentate  lobe  ;  the  posterior  end  becomes  bent  upon  itself,  form- 
ing the  uncinate  gyrus  (Figs,  260  and  261). 

The  Choroid  Fissure. — There  appears  in   man    at   about 


EMBRYOLOGY   OF   THE   CENTRAL   NERVOUS   SYSTEM.  543 

the  fifth  week  of  embryonic  life  an  infolding  into  the  lateral 
ventricle  of  the  dorsal  margin  of  the  median  surface  of  each 
hemispheral  wall,  which  occasions  an  arch-like  groove — the 
choroid  fissure.  This  fissure  extends  from  the  foramen  of 
Monro  to  the  apex  of  the  temporal  lobe.  It  embraces  the 
upper  convex  part  of  the  corpus  striatum  and  carries  into  the 
lateral  ventricle  a  fold  of  vascular  pia.  The  median  wall  which 
takes  part  in  the  formation  of  this  fissure  does  not  become 
thickened,  but  remains  very  thin,  consisting  only  of  a  single 
layer  of  epithelium  which  becomes  ultimately  adherent  to  the 
outer  surface  of  the  pia,  forming  a  covering  for  it.  The  very 
vascular  pia  now  grows  rapidly  within  the  lateral  ventricle,  and 
consists  of  a  number  of  villous  tufts  which  at  first  quite  fill  the 
cavity  of  the  ventricle,  but  later  there  is  a  considerable  free 
space  about  them.  These  vascular  folds  on  each  side  form  the 
choroid  plexuses  of  the  lateral  ventricle,  and  are  continuous 
with  the  choroid  plexus  of  the  third  ventricle  by  means  of  the 
foramen  of  Monro.  In  adult  life  the  choroid  plexus  of  each 
lateral  ventricle  becomes  confined  to  the  body  and  descending 
cornu  of  this  ventricle. 


DEVELOPMENT  OF  THE   COMMISSURAL   SYSTEM  OF  THE 
CEREBRAL   HEMISPHERES. 

At  about  the  third  month  of  fetal  life  fusion  occurs  between 
the  median  walls  of  the  cerebral  hemisphere  in  front  of  the 
terminal  lamina,  and  forms  a  triangular  septum  continuous 
behind  with  the  lamina  and  below  with  the  corpora  striata. 
The  fusion  of  the  walls  occurs  only  at  the  periphery  of  this 
area,  no  union  occurring  in  the  middle  portion.  This  middle 
portion,  which  forms  the  largest  part  of  the  area,  is  the  septum 
lucidum  and  contains  a  closed  cavity — the  fifth  ventricle.  From 
this  triangular  area  the  anterior  commissure,  the  corpus  callo- 
sum,  fornix,  and  septum  lucidum.  take  their  origin.  The 
anterior  commissure  is  first  made  manifest  by  a  local  thicken- 
ing just  beneath  the  Bogenfurche  and  in  front  of  the  foramen  of 
Monro,  and  consists  of  a  few  transverse  fibers. 

The  genu  of  the  corpus  callosum  is  formed  from  the  anterior 


544 


CENTRAL  NERVOUS  SYSTEM. 


part  of  the  triangular  area  ;  tlie  pillars  of  the  fornix  from  the 
posterior  part,  the  intermediate  or  larger  portion  located 
between  the  fornix  and  genu  of  the  corpus  callosum,  forms  the 
septum  lucidum. 

Between   the  fifth  and  sixth   months  the  union  of  the  hemi- 


par.occ. 


call.  mar. 


Fig.  262. — Fetal  Brain  ok  the  Beginning  of  the  Eighth  Month. — [Mihalkovics, 

from  Qua  in.) 
A.   From  above.     B.  From  the  side.     C.   Mesial  surface.     Jko.  Rolandic  sulcus.     Sy.   Sylvian 
fissure.      par.occ.    Parietooccipital.       calc.    Calcarine.       pr.c.    Precentral.      ///.   Parallel. 
int. par.    Intraparietal.      cnlLiiiar.    Callosomarginal.     iiiii\  uncus. 

spheres  has  extended  backward,  and  involves  that  part  of  the 
hemispheral  walls  between  the  Bogenfurche  above  and  the 
choroid  fissure  below,  and  is  called  the  marginal  arch,  gyrus  arcu- 
atus,  or  Randbogen.     From  the  anterior  part  of  this  curved  ridge 


EMBRYOLOGY   OF  THE   CENTRAL   NERVOUS   SYSTEM.  545 

originates  the  body  and  splenium  of  the  corpus  callosum  and 
the  fornix.  The  curved  groove  located  above  the  body  of  the 
corpus  callosum  is  the  remains  of  the  anterior  part  of  the 
Bogenfurche,  and  is  termed  the  fissure  of  the  corpus  callosum. 
The  posterior  part,  located  in  the  temporal  lobes,  forms  the 
hippocampal  fissure. 


THE  EVOLUTION  OF  THE  FISSURES  OF  THE  CEREBRAL 

HEMISPHERE. 

The  primary  fissures  are  all  formed  by  involutions  of  the 
hemispheral  walls,  with  the  production  of  corresponding  eleva- 
tions within  the  lateral  ventricles.  The  secondary  fissures  are 
mere  indentations  or  grooves  of  the  surface  of  the  brain  with- 
out the  production  of  internal  ridges  within  the  lateral  ventricles. 
The  primary  fissures  have  already  been  described  in  connection 
with  the  general  growth  of  the  hemispheral  vesicle.  They 
comprise  the  fossa  and  fissure  of  Sylvius  ;  the  arcuate  fissure,  or 
Bogenfurche ;  the  hippocampal,  the  parieto-occipital,  and  the 
calcarine  fissures. 

The  secondary  fissures  are  the  callosomarginal,  the  fissure 
of  Rolando,  precentral,  and  the  various  other  fissures  of  the 
frontal,  parietal,  and  occipital  lobes,  together  with  those  of  the 
island  of  Reil. 

The  callosomarginal  fissure  takes  its  origin  at  the  fifth 
month  of  fetal  life  in  front  and  above  the  corpus  callosum,  by  the 
union  of  two  or  three  smaller  fissures.  Posteriorly,  this  fissure 
is  prolonged  backward  and  upward  by  joining  a  few  shorter 
sulci,  terminating  just  dorsal  to  the  fissure  of  Rolando.  That 
part  of  the  hemispheral  mantle  between  the  callosomarginal  fis- 
sure and  the  corpus  callosum  is  called  the  gyrus  fornicatus. 

The  Fissure  of  Rolando. — This  fissure  usually  develops 
toward  the  end  of  the  fifth  month,  and  appears  as  two  distinct 
limbs  or  grooves — an  upper  and  a  lower.  The  lower  groove, 
much  the  larger,  has  a  slight  obHque  direction,  and  when  fully 
developed,  forms  the  lower  two-thirds  of  the  fissure.  It  reaches 
downward  almost  to  the  fissure  of  Sylvius.  Above,  it  is  sepa- 
rated  from   the  upper  groove  by  an  elevation  of  the   cerebral 

35 


5+6  CEN  TRAL  NERVOUS  SYSTEM. 

cortex  (mantle).  The  upper  groove  or  limb  is  much  shorter 
and  deeper  than  the  lower,  and  is  separated  from  the  marorin  of 
the  hemisphere  by  a  narrow  strip  or  cortex.  The  two  limbs  at 
hrst  ununited  soon  join  by  the  formation  of  a  groove  which  runs 
over  the  summit  of  the  intervening  elevated  portion  of  the  cor- 
tex. Later  in  the  course  ot  development  this  fissure  becomes 
much  deeper  and  the  elevated  portion  is  displaced  to  the  bot- 
tom of  it,  where  it  remains  as  a  permanent  elevation,  indicating 
the  point  of  junction  between  the  two  primitive  grooves  of 
which  this  fissure  is  composed.  The  fissure  of  Rolando  forms 
the  anatomic  division  between  the  frontal  and  parietal  lobes. 

The  precentral  sulcus  or  fissure  originates  at  the  end  of  the 
sixth  fetal  month  in  two  distinct  portions  located  in  front  of  the 
fissure  of  Rolando.  These  portions  usually  remain  entirely  dis- 
tinct from  each  other,  although  they  occasionally  unite.  Be- 
tween this  sulcus  and  the  fissure  of  Rolando  develops  the 
ascending  frontal  or  anterior  central  convolution. 

The  fissures  or  sulci  of  the  island  of  Reil  are  developed 
during  the  fifth  and  sixth  months  of  embryonic  life,  and  consist 
of  three  vertical  sulci  named  from  before  backward — the  pre- 
central, the  central,  and  the  postcentral.  The  precentral  sulcus 
appears  as  if  continuous  with  its  precentral  fissure,  the  central 
sulcus  with  the  fissure  of  Rolando,  and  the  postcentral  with  the 
intraparietal  fissure. 

The  various  fissures  of  the  frontal,  parietal,  temporal, 
and  occipital  lobes  are  formed  about  the  sixth  month  of  fetal 
life.  In  the  frontal  and  temporal  lobes  their  course  is  chiefly 
longitudinal,  while  in  the  parietal  and  occipital  lobes  their  course 
is  either  oblique  or  vertical.  These  fissures  serve  to  separate 
the  above-mentioned  lobes  into  gyri  or  lobules. 

The  development  of  the  interior  intraparietal  and  collateral 
fissures  are  worthy  of  separate  description. 

The  mte^"-  or  intraparietal  fissure  appears  at  the  sixth  month  as 
two  distinct  limbs — one  dorsal  to  the  fissure  of  Rolando  and  run- 
ning parallel  to  it ;  the  other  has  horizontal  course  below  the  mar- 
gin of  the  hemisphere.  The  two  sulci  join  during  the  eighth  month, 
to  form  the  main  fissure.  The  intraparietal  fissure  separates  the 
parietal  lobe  into  a  superior  and  an  inferior  parietal  lobule. 


EMBRYOLOGY   OF   THE   CENTRAL   NERVOUS   SYSTEM.  547 

The  collateral  or  occipitotemporal  fissiire  is  formed  at  the  sixth 
month.  It  consists  of  a  deep,  long,  horizontal  fissure  located  on 
the  median  surface  of  the  temporal  lobe  near  its  lower  margin, 
and  produces  an  eminence  in  the  descending  horn  of  the  lateral 
ventricle,  known  as  the  eminentia  collateralis,  or  pes  acces- 
sorius.  By  many  this  fissure  is  considered  to  be  an  infolding  of 
the  hemispheral  wall,  and  should  be  classified  with  the  primary 
fissures. 


DEVELOPMENT  OF  THE  CRANIAL  NERVES. 

The  cranial  nerve-roots  are  arranged  into  ventral  or  motor 
and  dorsal  or  sensory.  They  are  developed  in  a  manner  entirely 
similar  to  the  spinal  nerves.  The  neuroblasts  in  the  upper 
cervical  regfion  of  the  cord  form  on  each  side  two  distinct  long-i- 
tudinal  columns  of  cells,  which  are  continued  brainward  along 
the  floor  of  the  cerebral  vesicles,  as  far  forward  as  the  ventral 
part  of  the  mid-brain.  These  two  columns  of  neuroblasts 
correspond,  in  the  fully  developed  cord,  to  the  cell-groups  exist- 
ing in  the  ventral  and  lateral  horns,  and  hence  are  distinguished 
as  the  ventral  and  lateral  columns  of  (neuroblasts)  cells.  The 
neuroblasts  of  the  ventral  columns  give  origin  to  the  following 
pairs  of  motor  cranial  nerves — viz.  :  hypoglossal,  abducens, 
patheticus,  and  motor  oculi.  The  neuroblasts  of  the  lateral 
columns  form  the  spinal  accessory,  motor  divisions  of  the 
glossopharyngeal  and  pneumogastric  (nucleus  ambiguus),  the 
facial  and  the  motor  division  (portio  minor)  of  the  fifth  or  tri- 
geminus. 

The  sensory  fibers  of  the  cranial  nerves,  with  the  exception 
of  the  optic  and  olfactory,  are  developed  before  the  complete 
closure  of  the  neural  tube,  from  an  outgrowth  on  each  side 
called  the  neural  bands,  which  serve  to  connect  the  dorsal  part 
of  the  medullary  ridges  with  the  external  epiblast.  Soon  this 
connection  with  the  external  epiblast  is  lost,  and  the  two  neural 
bands  become  united  just  dorsal  to  the  point  of  junction  of  the 
medullary  ridges,  to  form  the  neural  canal.  There  is  thus  formed 
a  neural  crest,  which  extends  along  the  mid-dorsal  part  of  the 
neural  tube  as  far  brainward  as  the  ventral  part  of  the  mid-brain 


54S 


CENTRAL  NERVOUS  SYSTEM. 


root.  This  crest  posteriorly  is  continuous  with  the  neural  crest 
of  the  spinal  cord.  From  the  paired  outgrowths  of  the  neural 
crest  are  developed  the  sensory  ganglia  of  the  cranial  nerves, 
the  fibers  of  which  nerves  represent  the  peripheral  and  central 
processes  of  the  cells  of  these  ganglia.  These  ganglia  are  in 
order,  from  below  upward,  the  jugular,  the  petrosal,  the  genicu- 
late, the  auditory,  and  the  Gasserian.     They  give  origin,  respect- 


EiG.  263. — Sections  Across  the  Hind- brain  of  a  Human    Emuryo,  10  mm.  Long. — 

( His,  froJH   Qua  in . ) 

In  .\,  the  origin  of  the  spinal  accessory  and  hypoglossal  nerves  is  shown,  the  fibers  of  both  aris- 
ing from  groups  of  neuroblasts  in  the  basal  lamina  of  the  neural  tube.  In  B,  one  of  the 
roots  of  the  hypoglossal  is  still  seen,  and,  in  addition,  the  root  of  the  vagus  nerve.  This  is 
represented  as  in  part  arising  like  that  of  the  spinal  accessory  in  A,  from  a  group  of  neuro- 
blasts in  the  basal  lamina,  and  in  part  from  a  bundle  of  longitudinally  coursing  fibers  placed 
at  the  periphery  of  the  alar  lamina,  and  corresponding  in  situation  to  the  commencing  pos- 
terior white  columns. 


ively,  to  the  sensory  divisions  of  the  pneumogastric,  the  glosso- 
pharyngeal, the  facial,  the  auditory,  and  the  trigeminal  nerves. 

The  ganglia,  which  are  connected  with  the  sensory  cranial 
nerves,  have  the  same  histologic  formadon  as  do  the  posterior 
spina!  ganglia.  As  development  goes  on,  these  ganglia  shift 
their  posiuon  and  become  more  ventrally  located.* 


*  All  cells  of  the   cerebral   ganglia,  with  the  exception  of  those   of    the  auditory  ganglia, 
become,  later  in  development,  unipolar. 


EMBRYOLOGY   OF   THE   CENTRAL   NERVOUS   SYSTEM. 


549 


The  primitive  cerebral  ganglia  contain  embryonic  cells  bi- 
polar in  shape,  each  cell  possessing  a  central  and  a  peripheral 
axone.  The  central  axones  enter  the  cephalic  part  of  the  neural 
tube  as  sensory  cranial  nerve-fibers,  and  terminate  about  certain 
special  collections  of  nerve-cells  in  the  dorsal  zones  of  different 


m.c.v. 


Fig.  264. — Section   from   the  same  Embryo  at  the   Exit  of  the   Facial  Ner\e. 

(Several  sections  have  been  combined  to  form  this  figure.) — [His,  from  Qitain.) 
VI.   Fibers  of  sixth  nerve  taking  origin  from  group  of  neuroblasts  in  basal  lamina.      VII.G.g. 

Ganglion  geniculi  of  the  facial.      VIII.  G.i.c.   Intracranial  ganglion  of  auditory.      7 Y//.  G.v. 

Ganglion  vestibuli.       VIII.  G.c,  Ganglion  cochlese. 


segments  of  the  neural  tube.  These  groups  of  cells  form  for 
the  central  axones  (sensory  nerve-fibers)  terminal  end  nuclei 
(formerly  called  the  nuclei  of  origin  for  those  nerves)  ;  the  per- 
iphery (sensory)  axones  grow  outward  and  join  sensory  end 
organs. 

Central  sensory  axones  from  the  cells  of  the  ganglia  connected 
with  the  pneumogastric  and  glossopharyngeal  nerves  penetrate 


550  CENTRAL  NERVOUS  SYSTEM. 

the  medulla,  and,  curving-  downward,  form  on  each  side  two  oval 
bundles  of  descending  fibers — the  solitary  bundles.  These 
bundles  at  first  are  superficially  located,  but  later  become  dis- 
placed rather  deeply  inward,  and  may  be  seen  as  roundish 
bundles,  one  on  each  side,  slightly  ventrolateral  to  the  sensory 
end   nuclei  of  the  pneumogastric  and  glossopharyngeal  nerves. 


Fk;.  265. — Cranial  Nerves  of  a  Human  Embkyo,  10.2  mm.  Long, — [His,  from  (Jitain.) 
The  cranial  nerves  are  indicated  by  Roman,  the  spinal  nerves  by  Arabic,  numerals. 

cJi.  Cerebral  hemisphere,  th.  Thalamencephalon.  m.b.  IMid-brain.  Mx.  Maxillary  process. 
Mn.  Mandibular  arch.  Ny.  Ilyoid  arch.  The  facial  nerve  is  seen  to  send  a  branch 
(chorda  tympani)  across  the  hyomandibular  cleft'.  G.g.  Gasserian  ganglion,  e.g.  Ciliary 
ganglion,  v.  Vestibular,  and  c,  cochlear,  part  of  auditory,  g.p.  Ganglion  petrosum  of 
glossopharyngeal,  g.j.  Ganglion  jugulare  of  vagus.  An  anastomosis  is  seen  between 
these.  g-t>'-  Ganglion  trunci  of  vagus.  F.  Ganglion  described  by  Froriep  as  belonging 
to  the  hypoglossal,  r.d.  Ramus  descendens  of  hypoglossal,  of.  Otic  vesicle.  The  eye 
is  also  represented,  and  a  part  of  the  heart. 


DEVELOPMENT  OF   THE  OLFACTORY  LOBE. 

The  olfactory  lobe  is  formed  about  the  fourth  week  of 
embryonic  life  as  a  hollow  protrusion  or  fold  of  the  hemi- 
spheral  wall,  extending  forward  from  the  ventral  part  of  the 
under  surface  of  the  hemispheric  vesicle,  to  form  a  distinct 
longitudinal  ridge,  separated  by  an  internal  groove.     This  pro- 


EMBRYOLOGY   OF   THE   CENTRAL   NERVOUS    SYSTEM.  551 

truslon  soon  partially  separates  from  the  hemisphere,  to  form  a 
blind,  tubular-like  process  which  is  only  connected  at  its  base  or 
posterior  part  with  the  hemispheral  wall,  its  cavity  communicat- 
ing with  the  lateral  ventricle,  of  which  it  is  a  part.  The  primitive 
olfactory  lobe  is  crossed  by  the  primary  fissure,  or  Bogenfurche 
of  His,  which  divides  it  into  a  ventral  and  a  dorsal  part.  The 
ventral  part  gives  origin  to  the  olfactory  tr^ct  and  bulb  and  the 
trigonum  olfactorium  ;  from  the  dorsal  part  is  developed  the  inner 
and  outer  olfactory  roots,  the  peduncles  of  the  corpus  callosum, 
and  the  anterior  perforated  space. 

The  first  process  in  the  development  of  the  olfactory  nerves 
is  the  separation  of  the  olfactory  plates,  which  are  the  thickened 
parts  of  the  epiblast  united  to  the  walls  of  the  fore-brain  vesicle. 
This  takes  place  by  an  ingrowth  of  a  process  of  the  mesoblast. 
The  second  stage  is  the  formation,  by  karyokinesis,  of  neuro- 
blasts from  the  ectodermal  cells  of  the  olfactory  plates.  These 
neuroblasts  soon  assume  a  bipolar  shape,  and  together  form  on 
each  side  a  ganglion  which  lies  between  the  epiblast  (olfactory 
plate)  and  the  olfactory  lobe.  At  the  end  of  the  fifth  week 
this  ganglion  grows  upward  and  backward,  and  becomes  located 
in  a  groove  just  dorsal  to  the  anterior  division  of  the  olfactory 
lobe.  It  then  grows  ventrally,  and  surrounding  the  olfactory 
bulb,  becomes  fused  with  it,  thus  forming  a  superficial  layer 
around  it.  The  exact  development  of  the  peripheral  olfactory 
nerves  is  not  at  present  known.  According  to  His,  the  bipolar 
cells  of  the  above-described  ganglia  lengthen  at  each  pole  into 
centripetal  or  central  olfactory  nerve-fibers,  and  centrifugal  or 
peripheral  olfactory  nerve-fibers,  the  latter  being  distributed  to 
the  olfactory  mucous  membrane.  It  seems  more  reasonable  to 
believe  that  this  ganglionic  mass  which  forms  the  superficial 
gray  layer,  capping  the  ventral  half  of  the  olfactory  bulb,  gives 
oriein  to  the  mitral  cells,  whose  axones  form  the  central  olfac- 
tory  nerve-fibers  and  whose  dendrites  assist  in  the  formation  of 
the  olfactory  glomeruli,  the  peripheral  olfactory  apparatus  con- 
sisting of  the  olfactory  cells  of  the  Schneiderian  mucous  mem- 
brane with  their  processes,      (See  page  325.) 


552  CENTRAL  NERVOUS  SYSTEM 

DEVELOPMENT  OF  THE  RETINA  AND  OPTIC  NERVES. 

riie  optic  vesicles  are  developed  as  hollow  protrusions,  one 
from  each  side  wall  of  the  primary  fore-brain.  It  will  be 
remembered  that  the  ventral  wall  of  the  fore-brain  expands, 
and  growing  rapidly,  forms  the  cerebral  hemispheres,  thus 
changing  the  position  of  the  fore-brain  so  that  it  becomes 
located  between  the  prosencephalon  and  the  mid-brain,  and  is 
called  the  inter-  or  between-brain.  Hence,  the  optic  vesicles 
are  attached  on  each  side  to  the  ventral  wall  of  the  inter-brain, 
just  in  front  of  the  infundibular  region.  The  distal  part  of  each 
optic  vesicle  enlarges  upward  and  outward,  while  the  proximal 
hollow  part  becomes  narrowed  and  is  connected  with  the  ven- 
tral wall  of  the  brain.  This  narrow  part  is  called  the  stalk,  or 
pedicle  of  the  optic  vesicle,  and  is  the  rudiment  of  the  optic 
nerve.  The  most  prominent  part  of  the  optic  vesicle  joins  the 
adjacent  external  epiblast,  which  becomes  thickened  and  is 
thrust  inward,  pushing  before  it  a  part  of  the  front  wall  and 
pedicle  of  the  opdc  vesicle.  The  front  wall  of  the  optic  vesicle 
is  so  completely  invaginated  that  it  nearly  meets  the  posterior 
wall,  and  causes  an  almost  complete  obliteration  of  the  cavity 
of  the  optic  vesicle.  The  concavity  thus  formed,  containing  the 
involuted  epiblast,  is  called  the  optic  cup.  The  anterior  or 
inner  wall  of  this  cup  becomes  much  thickened,  to  form  the 
retina,  while  the  posterior  or  outer  wall  remains  thin,  and  has 
deposited  within  its  epithelial  cells  pigment,  forming  the  pig- 
ment layer  of  the  choroid.  This  hollow  involuted  portion  of 
the  epiblast  forms  the  rudiment  of  the  lens  and  becomes 
separated  from  the  adjacent  external  epiblast  by  the  closure  ol 
its  mouth,  remaining  within  the  cavity  of  the  optic  cup  close  to 
its  anterior  wall.  Later,  owing  to  the  more  rapid  growth  of  the 
walls  of  the  optic  cup  and  the  slow  growth  of  the  lens,  it  becomes 
displaced  forward  and  occupies  the  mouth  of  the  cup,  and  has 
developed  between  it  and  the  thickened  anterior  wall  of  the  cup 
or  retina,  the  vitreous  humor. 

During  the  time  of  the  invagination  of  the  epiblast  to  form 
the  lens,  a  groove  is  formed  along  the  lower  border  of  the  optic 
vesicle,  extending  backward  from  the  epiblast  to  the  stalk  of  the 


Fig.  266,  B. — Brain  of  Human  Embryo 
OF  Three  Weeks.  Showing  the  primary- 
optic  vesicles  as  outgrowths  from  the  fore- 
brain. — lyHis,froj}i  Quain.) 


Fig.  266,  A. — Brain  of  Chick  of  Second 

Day,  Viewed  from  Below,  to   Show 

THE  Formation  of  the  Optic  Vesicles 

BY  Outgrowth  of  the   Side  of  the 

Fore-brain,  and  at  the  Same  Time  by 

THE  Folding  Over  of  the  Enlarged    . 

Part,  the  Production  of  a  Grooving 

or    Cupping    of    the   Vesicles. — [His, 

from  Quain  ^j 
I,  4,  5.  Fore-,  mid-,  and  hind-brain.      2.   Optic  vesicle.      3.   Infundibulum. 


Fig.  267. — Side  View  of  Anterior 
Part  of  Brain  of  More  Ad- 
vanced Human  Embryo.  Showing 
the  primary  optic  vesicle  folded  and 
cupped.  — {^His,  from  Quain. ) 

I.  Cerebral  hemisphere  (part  of).  2. 
Olfactory  lobe.     3.  Optic  cup. 


Fig.  268.- — Side  View  of  the  Same  Part  of 
the  Brain  in  a  still  more  Advanced  Em- 
bryo, THE  Eye  Having  Been  Cut  Away. — 
[His,fro7?i  Quain.) 

r.  Cerebral  hemisphere.  2.  Anterior  part  of  the  olfac- 
tory lobe.  3.  Cut  end  of  optic  stalk,  showing  the 
manner  in  which  it  is  folded.    4.   Tuber  cinereum. 


55: 


EMBRYOLOGY  OF  THE  CENTRAL  NERVOUS  SYSTEM. 


555 


vesicle,  whose  walls  do  not  coalesce,  there  remaining  a  cleft  or 
fissure  which  receives  the  name  of  the  choroid  fissure  ;  through 
this  fissure  a  portion  of  vascular  mesoblastic  tissue  surround- 
ing the  optic  vesicle  gains  entrance  to  the  cavity  of  the  optic 
cup  behind  the  lens,  and  forms  the  vitreous  humor.  This 
choroid  fissure  soon  becomes  obliterated  by  the  coalescence  of 
its  walls,  and  thus  the  cavity  of  the  optic  vesicle  is  completely 
walled  in,  and  is  filled  with  the  vitreous  humor. 


Fig.  269. — Rabbit  Embryo  of  Ten  and 
One-half  Days;  Section  of  the  Lens 
Anlage. — i^From  Mitiot.) 

mes.  Mesoderm.  P.  Pigment  layer.  R. 
Retina.     L.  Lens.     Ec.   Ectoderm. 


Fig.  270. — Vertical  Section  of  the  Eye 

of   a    Chick   Embryo    of    the   Third 

Day. — [From  Minot.) 
Ec.  Ectoderm.    L.  Lens.    Ret.  Retina.     Cho. 

Choroid  layer.     Md.   Wall  of  brain.      Mes. 

Mesenchyma.     X  ^28  diam. 


The  closure  of  this  fissure  begins  in  front  and  gradually  pro- 
ceeds backward  toward  the  retina  ;  a  small  portion  remains  open, 
through  which  passes  the  arteria  centralis  retina,  which  courses 
inward  to  the  concavity  of  the  retina,  where  it  branches,  som.e 
branches  passing  through  the  vitreous,  and  being  distributed  to 
the  posterior  surface  of  the  lens,  producing  the  tunica  vasculosa. 
The  mesoblast  which  surrounds  the  optic  cup,  owing  to  increase 
in  size  of  the  latter,  becomes  condensed  and  forms  for  it  a  dis- 


555 


CENTRAL  NERVOUS  SYSTEM. 


tinct  investment,  this  being-  the  outline  of  the  eyeball.  The 
portion  of  this  investment  within  the  cavity  of  the  optic  cup  and 
close  to  the  retina  forms  the  choroid,  while  the  external  ])ortion 
develops  into  the  sclerotic  coat. 

The  process  of  mesoblast  which  grows  in  between  the  lens 
and  the  external  epiblast  has  developed  within  it  a  cavity  which 
separates  the  mesoblastic  process   into   two   layers,  an  anterior 


gi.Vs- , 


^>v^*-'t^V':  ■*!••.•::* '-^V 


tlLV 


Fig.  271. — Rabbit  Embryo  of  Thirteen  Days;   Section  of  the  Eye. — {From  Mhiot.) 

N.  Optic  nerve.      P.   Pigment  layer.      R.   Retina.     Ec.  Ejiidermis.     L.   Lens.     tu.v.  Tunica 

vasculosa.      mes.   Mesenchyina. 


and  a  posterior.  From  the  anterior  is  developed  the  cornea, 
with  the  exception  of  its  epithelium,  while  the  posterior  layer 
forms  the  iris.  The  cavity,  at  first  between  the  two  layers,  but 
now  located  between  the  cornea  and  lens,  is  called  the  anterior 
chamber,  and  contains  the  aqueous  humor. 

The  retina  is  developed  from  the  inner  (really  the  anterior) 
wall  of  the  optic  cup.      The  external  (outer  or  posterior)  wall 


EMBRYOLOGY    OF   THE    CENTRAL   NERVOUS    SYSTEM.  557 

becomes  thinned,  has  pigment  deposited  within  its  cells,  and 
forms  the  pigment  layer  of  the  retina  (choroid).  Separating  the 
retina  proper  from  the  pigment  layer  is  the  membrana  limitans 
externa.  The  construction  of  the  retina  is  not  unlike  that  of  the 
wall  of  the  embryonal  brain,  consisting  at  first  of  several  layers 
of  elongated,  nucleated  spindle  cells,  which  are  transformed 
partly  into  nerve-cells  and  fibers,  and  partly  into  neuroglia  cells 
and  fibers,  the  latter  forming  the  so-called  sustentacular  or  sup- 
porting tissue.  The  retina  grows  rapidly  in  thickness ;  this  is 
due  to  a  multiplication  of  its  cells,  which  become  arranged  into 
three  layers,  corresponding  to  similar  layers  in  the  walls  of  the 
embryonal  nervous  system.  These  are  the  ependymal  layer  or 
outer  part,  the  mantel  or  intermediate  layer,  and  the  Rand- 
schleier-or  layer  of  nerve-fibers.  The  layer  of  nerve-fibers  is 
separated  from  the  vitreous  by  the  membrana  limitans  interna. 

The  cells  of  the  ependymal  layer,  which  are  located  next  the 
membrana  limitans  externa,  form  the  outer  nuclear  layer,  the 
layer  of  rods  and  cones,  and  possibly  the  molecular  layer  and 
the  inner  nuclear  layer.  The  cells  corresponding  to  the  middle 
or  mantel  layer  give  origin  to  the  inner  molecular  layer  and  the 
layer  of  ganglionic  nerve-cells.  The  inner  layer,  or  Rand- 
schleier,  is  the  layer  of  nerve-fibers.  The  rods  and  cones  are 
developed  from  elongated  sensory  cells  in  the  outer  nuclear 
layer. 

The  rods  and  cones  of  the  retina  are  developed  in  man  at 
birth,  but  in  all  animals  that  are  born  blind  they  are  probably 
not  developed  until  after  birth.  They  first  appear  as  small  and 
large  roundish  projections  over  the  surface  of  the  external  limit- 
ing membrane,  the  small  projections  being  the  cones,  the  large 
ones,  the  rods.  Each  of  these  projections  is  an  outgrowth  of 
cells  which  form  the  outer  nuclear  layer  of  the  retina.  They 
become  elongated  and  penetrate  the  pigment  layer,  in  which 
their  tips  become  embedded. 

The  Optic  Nerves. — The  hollow  optic  stalks,  or  peduncles, 
of  the  optic  vesicles  which  are  attached  to  the  ventral  part  of 
the  inter-brain  become  solid  by  the  growth  of  their  walls  and  the 
consequent  obliteration  of  their  cavities.  Each  optic  stalk  is 
continuous  anteriorly  with  the  retina,  and  receives  from  the  cells 


558  CENTRAL  NERVOUS  SYSTEM. 

of  its  ganglionic  layer  many  axones  which  grow  inward  (cen- 
tripetal fibers)  into  the  optic  stalk,  and  finally  reach  the  primary 
optic  ganglia  of  the  same  and  the  opposite  side,  terminating  in 
arborizations  about  their  nerve-cells.  The  crossed  fibers  form 
a  chiasm  (optic  chiasm)  in  front  of  the  infundibulum  by  passing 
through  a  ridge  formed  between  the  roots  of  the  optic  stalks..  In 
many  of  the  lower  animals  this  decussation  is  complete,  but  in 
man  it  is  incomplete.  The  optic  stalk  also  contains  fibers, 
axones  of  the  cells  of  the  primary  optic  ganglia,  which  grow 
outward  (centrifugal  fibers)  through  the  optic  stalk  and  ulti- 
mately terminate  about  the  cells  of  the  retina. 

The  solid  optic  stalks  contain,  at  the  time  of  the  obliteration 
of  their  cavities,  radially  placed  neuroglia  cells  whose  processes 
form  a  meshwork  through  which  the  previously-mentioned 
nerve-fibers  pass. 


CHAPTER  XIV. 

TECHNIC   OF  THE   MACROSCOPIC   AND   MICRO- 
SCOPIC EXAMINATION  OF  THE  BRAIN  AND 
SPINAL  CORD. 

In  order  to  expose  the  brain,  an  incision  through  the  scalp 
should  be  made,  extending  from  one  mastoid  process  to  the 
other.  Use  a  short  scalpel,  and  cut  from  within  outward  to 
prevent  injury  to  the  hair.  If  this  is  found  very  heavy,  as  in 
some  women,  it  is  wise  to  part  it  at  a  line  across  the  vertex, 
from  mastoid  to  mastoid,  and  then  braid  each  fold,  one  for- 
ward, the  other  backward,  protecting  them  from  soiling  by 
covering  with  gauze.  Dissect  the  anterior  flap  free  from  the 
temporal  muscles  and  carry  it  forward  nearly  to  the  margin  of 
the  orbit.  The  posterior  flap  should  be  dissected  back  as  far  as 
the  occipital  protuberance. 

The  bone  should  now  be  bared  of  the  temporal  muscles  and 
pericranium  along  the  line  of  incision,  which  extends  in  a  circu- 
lar manner  across  the  frontal  bones  behind  the  orbital  ridges, 
thence  downward  and  backward  across  the  temporal  and 
occipital  bones  to  the  occipital  protuberance.  Care  should  be 
taken  not  to  saw  through  the  inner  table  for  fear  of  injuring 
the  brain-tissue.  The  incision  can  be  finished  by  severing  the 
inner  table  with  the  chisel  and  mallet.  When  the  calvaria 
is  nearly  free,  it  may  be  removed  by  inserting  into  the  anterior 
part  of  the  incision  a  blunt  hook  and  pulling  sharply  backward. 

With  a  blunt-pointed  scissors  cut  through  the  dura  along  the 
lines  corresponding  to  the  incision,  and  fold  each  side  of  the 
dura  inward,  thus  exposing  the  hemispheres  ;  next,  separate 
the  falx  cerebri  from  the  crista  galli  by  passing  a  knife  down- 
ward on  the  left  side  to  the  falx,  and  then  cut  to  the  right  until 
it  gives  way,  pull  the  dura  gently  backward  and  let  it  hang. 

559 


56o  LKMRAL  NKRVOUS  SYSTEM. 

The  brain  being  exposed,  with  one  hand  push  backward  the 
frontal  lobes  and  cut  the  exposed  cranial  nerves  and  carotid 
arteries  close  to  their  foramina.  Then  lift  each  temporal  lobe 
in  order,  and  cut  throiigli  the  tentorium  cerebelli  close  to  its 
attachment  to  the  petrous  bone.  Supporting  the  convexity  with 
the  palm  of  one  hand,  tilt  the  brain  backward,  separating  it  from 
the  cord  as  low  down  as  possible,  after  having  severed  the 
cranial  nerves  from  their  points  of  attachment  to  the  pons  and 
medulla.  The  brain  now  being  free,  can  be  lifted  gently  out  of 
the  skull. 

Of  the  several  methods  in  use  for  sectioning  the  fresh  brain, 
those  described  by  Virchow  and  Pitres  are  all  that  could  be 
desired  to  determine  the  location  and  extent  of  cerebral  lesions. 
The  method  of  Dejerine,  while  not  so  commonly  used,  is  better 
for  preserving  fresh  sections  for  subsequent  microscopic  study. '=' 


VIRCHOW'S  METHOD. 

In  this  method  the  brain  is  placed  on  a  flat  surface,  with  its 
base  down  ;  the  hemispheres  are  then  carefully  spread  apart  so 
as  to  expose  the  corpus  callosum.  A  longitudinal  incision  is 
now  made,  close  to  the  margin  of  the  hemisphere,  through  the 
corpus  callosum,  into  the  body  of  the  lateral  ventricle,  care  being 
taken  not  to  injure  the  basal  ganglia  ;  the  incision  is  then 
extended  forward  and  backward  so  as  to  expose  the  whole 
length  of  the  ventricle  with  its  anterior  and  posterior  cornua. 
A  second  lonoritudinal  incision  is  made  outside  of  the  basal 
ganglia,  from  one  end  of  the  hemisphere  to  the  other.  Incisions 
of  a  like  character  are  to  be  made  in  the  hemisphere  of  the 
opposite  side.  As  many  more  longitudinal  incisions  through 
each  hemisphere  can  be  made  as  seems  desirable,  care  being 
taken  not  to  cut  through  the  pia,  as  this  membrane  serves  to 


*  Method  of  Dejerink. — The  brain,  resting  on  its  upper  surface,  is  first  sectioned  by  a  com- 
plete transverse  incision  through  it,  the  incision  starting  through  the  ventral  part  of  the  pons 
just  in  front  of  the  trigeminal  nerves.  The  occipital  and  frontal  lobes  are  separated  by  trans- 
verse incisions  beginning  at  each  extremity  of  the  corpus  callosum.  A  horizontal  cut  through 
each  hemisphere  is  now  made  just  above  the  caudate  nucleus.  If  it  is  desirable  to  separate  the 
attached  cerebral  hemispheres,  this  may  be  done  by  an  incision  through  the  corpus  callosum  and 
middle  of  the  interpeduncular  space. 


EXAMINATION  OF  THE  BRAIN  AND  SPINAL  CORD— TECHNIC.         561 

hold  the  sections  together,  so  that  after  the  brain  is  sectioned 
they  can  be  properly  replaced.  The  remains  of  the  corpus 
callosumand  fornix  are  next  cut  through  and  reflected  backward 
by  passing  the  knife  through  the  foramina  of  Monro,  thus 
exposing  the  velum  interpositum  and  choroid  plexuses.  By 
pulling  back  the  velum  interpositum,  the  third  ventricle  is 
brought  into  view.  The  corpora  quadrigemina  may  be  seen  by 
cutting  through  the  posterior  pillars  of  the  fornix.  Frontal  or 
transverse  sections  are  now  made  from  before  backward  through 
the  basal  ganglia.  A  longitudinal  section  is  next  made  through 
the  pineal  gland,  corpora  quadrigemina,  and  worm  (vermis)  of 
the  cerebellum,  exposing  the  aqueduct  of  Sylvius  and  the  fourth 
ventricle.  The  cerebellum  is  further  divided  by  making  median 
horizontal  sections  radiating  from  its  peduncles.  The  brain  is 
now  turned  over  and  the  pons  and  medulla  are  divided  into 
sections  by  several  transverse  incisions. 

This  method  of  Virchow  is  not  suitable  for  further  microscopic 
study,  because  the  brain  is  already  too  much  cut  up.  The  fol- 
lowing method  of  Pitres  is  well  adapted  for  the  gross  and  micro- 
scopic study  of  the  sections  : 


PITRES'   METHOD. 

In  this  method  the  lateral  ventricles  are  exposed  in  the  same 
manner  as  in  Virchow's  method. 

The  pons,  medulla,  and  cerebellum  are  separated  from  the 
hemispheres  by  cutting  transversely  through  the  crura  cerebri, 
and  may  be  sectioned  in  the  same  manner  indicated  in  Vir- 
chow's method.  The  cerebral  hemispheres  are  detached  from 
one  another  by  a  longitudinal  Incision  through  the  third  ven- 
tricle. Each  hemisphere  is  further  divided  into  the  following 
six  sections  by  incisions  made  parallel  to  the  fissure  of  Ro- 
lando and  extending  completely  through  the  gray  and  white 
matter : 

1.  Prefrontal  Section. — This  section  is  made  through  the 
frontal  lobe,  five  centimeters  ventral  to  the  fissure  of  Rolando. 
It  shows  the  gray  and  white  matter  of  that  lobe. 

2.  The  pediculofrontaL  section  passes  through  the  foot  or  base 

35 


562  CENTRAL  XKRVOUS  SYSTEM. 

of  the  tliree  frontal  convolutions,  showing  the  ventral  parts  of 
the  insula  or  island  of  Reil,  the  lenticular  and  caudate  nuclei,  and 
the  internal  capsule. 

3.  The  frotital  section  is  throuoh  the  ascending  frontal  convo- 
lution, and  shows  the  optic  thalamus  and  lenticular  and  caudate 
nuclei,  the  internal  and  external  capsules,  the  claustrum,  the 
descendinij  horn  of  the  lateral  ventricle,  and  the  insula. 

4.  The  parietal  section  passes  through  the  ascending  parietal 
convolution,  and  shows,  in  addition  to  the  parts  shown  in  the 
frontal  section,  the  hippocampus  major  divided  transversely. 

5.  The  pediciilopai'ietal  section  is  made  through  the  parietal 
lobe,  three  centimeters  dorsal  to  the  fissure  of  Rolando,  and 
shows  the  tail  of  the  caudate  nucleus  and  the  dorsal  part  of 
the  optic  thalamus. 

6.  TJie  occipital  section  is  through  the  occipital  lobe,  one  cen- 
timeter anterior  to  the  external  parieto-occipital  fissure,  and 
shows  the  gray  and  white  matter  of  the  occipital  lobe. 

If  it  is  not  advisable  to  section  the  brain  in  its  fresh  state,  it 
may  be  permitted  to  harden  in  a  ten  per  cent,  solution  of  forma- 
lin for  a  w^eek  or  ten  clays,  when  it  can  be  divided  into  a  series 
of  frontal  or  satrittal  sections. 

This  method  is  particularly  useful  for  the  study  of  the  gross 
or  microscopic  appearance  and  situation  of  lesions.  It  preserves 
the  normal  difference  in  color  betw^een  the  gray  and  wdiite  mat- 
ter, and  permits  of  staining  by  the  methods  of  Weigert,  Golgi, 
Xissl,  and  Van  Gieson.  Another  solution  which  will  be  found 
useful  to  harden  the  cerebrospinal  axis  entire  is  Orth's  fluid. 
It  may  be  changed  each  day  for  three  days.  At  the  expiration 
of  three  weeks  the  hardening  is  complete,  when  it  may  be 
transferred  to  alcohol.  This  method  permits  of  staining  after 
the  before-mentioned  methods,  save  Nissl's.  An  excellent  and 
well-known  preservative  solution  for  hardening  the  brain  or 
spinal  cord  is  Miiller's  fluid.  This  fluid  consists  of  potassium 
bichromate  2  to  2^^  parts,  sodium  sulphate  i  part,  water  100 
parts.  This  fluid  should  be  renewed  each  day  for  a  week  ;  it 
takes  from  six  weeks  to  three  months  to  harden  properly. 
Specimens  are  then  transferred  directly  into  alcohol.  This 
method  of    hardening    is    particularly   useful    for    staining,   by 


EXAMINATION  OF  THE  BRAIN  AND  SPINAL  CORD— TECHNIC.  563 

Weigert's  method,  the  Cox-Golgi,  or  by  Berkley's  modification 
of  the  Golgi  method. 

Orth's  Fluid. 

Potassium  bichromate, 2  to  2.5  parts 

Sodium  sulphate, I  part 

Water, loo  parts 

Formaldehyd  (forty  per  cent,  solution),       10  parts. 


THE   REMOVAL  OF  THE  SPINAL  CORD. 

To  remove  the  spinal  cord,  the  body  is  placed  with  the  face 
downward,  the  head  projecting  over  the  end  of  the  table,  with 
the  chest  elevated  by  placing  a  block  beneath  it.  An  incision 
is  now  made  over  the  spinous  processes  of  the  vertebra  to  the 
bone  extending  from  the  occipital  protuberance  to  the  sacrum. 
The  soft  parts  covering  the  vertebral  lamina  are  dissected  away 
from  each  side.  The  vertebral  lamina  are  sawed  through  or 
cut,  by  means  of  a  chisel,  from  the  upper  cervical  to  the  lower 
lumbar.  The  lamina  being  free,  the  cervical  arches  are  cut 
through  with  a  chisel  and  the  spinal  processes  of  the  lumbar 
vertebra  are  freed  from  their  ligaments  in  the  same  manner. 
The  dorsal  portion  of  the  spine  with  its  processes  can  now  be 
stripped  away  its  whole  length.  The  nerve-roots  are  severed 
on  each  side  with  a  narrow-bladed  knife.  The  membranes  and 
cord  are  cut  across  hio-h  in  the  cervical  remon  ;  the  cord  is  then 
lifted  from  its  position  by  taking  hold  of  the  dura  with  the 
forceps  and  separating  it  from  above  downward  with  a  scissors 
and  the  handle  of  a  scalpel.  After  the  cord  is  removed,  the 
dura  is  cut  through  longitudinally  both  in  front  and  behind. 
The  cord  being  supported  by  the  fingers,  is  divided  by  a  sharp 
scalpel  into  a  number  of  transverse  sections  two  centimeters 
apart. 


DIFFERENTIAL      STAINS      FOR    THE     VARIOUS     ELE- 
MENTS   OF    THE    NERVOUS    SYSTEM. 

In   this    description    mention   will    be    made  of  some  of  the 
methods  which  have  been  found  particularly  useful  in  staining 


564  CENTRAL  NERVOUS  SYSTEM. 

the  elements  of  the  nervous  system.  If  the  student  is  desirous 
of  becoming-  familiar  with  all  the  methods  now  in  use,  he  should 
consult  the  excellent  works  of  V.  Kahlden,  B.  Pollack,  IMallory 
and  Wright.  The  differential  stains  may  be  divided  into  those 
useful  for  staining  nerve-cells  and  their  protoplasmic  granules, 
those  for  delineating  the  contour  of  cell-bodies  and  their  proto- 
plasmic processes,  those  for  myelin  sheaths,  and  those  for 
neuroglia  tissue.  These  do  not  include  certain  general  stains  to 
be  described  hereafter,  which  are  not  considered  differential  in 
character. 

Staining  of  Nerve-cells  after  the  Method  of  Nissl. — 
Small  cubes  of  fresh  nervous  tissue  i  to  ly,  centimeters  in 
diameter,  after  having  been  hardened  in  ninety-six  per  cent, 
alcohol,  are  fastened  to  blocks  by  dipping  the  base  of  each  cube 
into  thick  celloidin.  Sections  are  cut  very  thin  and  placed  into 
ninety-six  per  cent,  alcohol.  They  are  stained  for  about  five 
minutes  in  the  following  solution  of  methylene-blue,  which  has 
been  previously  heated  over  a  flame  until  it  bubbles  : 

Methylene-blue  (H.  patent), 3.75 

Venetian  soap, 1.75 

Aquadestillata,  .        looo 

They  are  next  differentiated  in  anilin  oil  lo  parts,  alcohol 
(ninety-six  per  cent.)  90  parts,  until  the  color  ceases  to  be  dis- 
charged in  coarse  clouds.  Each  section  is  now  placed  on  a 
glass  slide  and  thoroughly  and  carefully  dried  with  filter-paper, 
and  then  cleared  in  oil  of  cajuput,  again  dried  and  washed  with 
a  little  benzine  ;  lastly,  add  a  few  drops  of  benzine  collophonium, 
and  pass  slide  through  a  flame  to  drive  off  excess  of  benzine  ; 
this  ienites  the  benzine,  which  should  be  immediatelv  blown  out. 
This  process  should  be  repeated  a  few  times  until  all  the  ben- 
zine is  evaporated  ;  heat  the  slide,  and  cover  with  a  thin  cover- 
glass.  By  this  method  the  cell-body  with  its  protoplasmic  gran- 
ules are  beautifully  stained. 

To  Stain  Nerve-cells  with  Thionin. — (i)  Harden  in  ninety 
percent,  alcohol,  then  in  absolute  alcohol,  or  in  formalin  followed 
by  alcohol;  (2)  embed  specimens  in  celloidin  or  paraffin  ;  (3) 
stain  sections  for  five  minutes  in  concentrated  solution  of 
thionin  ;    (4)  wash  quickly  in  water  ;   (5)   differentiate    in    anilin 


EXAMINATION  OF  THE  BRAIN  AND  SPINAL  CORD— TECHNIC.        565 

oil  I   part,  absolute  alcohol   9   parts  ;   (6)   clear   in  oil   cajuput ; 
(7)   then  in  xylol;   (8)  xylol  balsam. 

Method  of  Bevan  Lewis. — This  method  is  well  adapted 
for  the  study  of  the  different  cell-layers  of  the  cortex  as  they 
normally  exist.  The  nerve-cells,  with  their  protoplasmic  pro- 
cesses retaining  their  original  size  and  shape,  not  having  been 
altered  by  hardening  reagents.  This  method  also  stains  the 
axis-cylinder  processes,  neuroglia  tissue,  pia  mater,  and  the 
connective  tissue  about  blood-vessels. 

A  piece  of  brain-tissue  about  one  inch  in  length  and  three- 
fourth's  of  an  inch  thick  is  removed,  care  being  taken  to  include 
the  entire  cortex  and  the  overlying  pia  mater.  It  is  then  cut 
into  fine  sections  by  means  of  a  freezing  microtome.  These 
sections  are  conveyed  on  the  blade  of  the  microtome  knife  to 
distilled  water,  and  then  immediately  floated  on  to  glass  slides, 
the  superfluous  water  being  permitted  to  drain  away.  The  sec- 
tions are  then  covered  for  a  few  seconds  with  a  one-fourth  of 
one  per  cent,  solution  of  osmic  acid.  This  short  contact  with 
osmic  acid  simply  fixes  the  myelin  without  producing  a  distinct 
osmic  acid  stainine.  The  sections  are  now  washed  in  distilled 
water  for  five  or  ten  minutes.  Each  section  is  again  floated  on 
to  a  glass  slide,  the  excess  of  water  being  drained  off.  They 
are  stained  on  the  slide  for  from  a  half  to  one  hour  with  a  one 
fourth  of  one  per  cent,  solution  of  anilin  blue-black.  They  are 
then  washed  in  water  and  again  floated  on  glass  slides,  where 
they  are  permitted  to  dry  by  exposure  to  the  atmosphere. 
When  thoroughly  dry,  they  are  mounted  in  Canada  balsam. 
The  nerve-cells  and  fibers  are  stained  a  bluish-gray  color. 

The  following  method,  a  modification  of  Kronthal's,  is  a 
very  useful  one,  not  only  to  show  the  nerve  cell-body  and  its 
protoplasmic  granules,  but  stains  the  axone  and  the  dendritic 
processes,  as  well  as  the  neuroglia.  It  stains  capillary  blood- 
vessels very  beautifully.  Fresh  nervous  tissue  (brain  or  cord) 
is  obtained,  and  a  small  bit  of  the  gray  matter  is  placed  on  a 
cover-glass,  and  is  covered  by  another  cover-glass.  The  two 
cover-slips  are  pressed  together  so  as  to  spread  the  tissue  out 
into  as  thin  a  layer  as  possible.  The  separated  covers  are  per- 
mitted to  dry  in  the  air,  and  are  stained  for  fortv  minutes  in  a 


566  CENTRAL   NERVOUS  SYSTEM. 

saturated  solution  of  methylene-blue,  then  waslied  in  water  lor 
a  minute  or  two,  dried  in  the  air,  and  mountetl  in  Canada 
balsam. 

Golgi's  Method  for  Staining  Nerve-cells  and  Their 
Processes. — This  method  depends  for  its  efficacy  upon  the 
precipitation  of  silver  or  mercur)-  salts  in  the  protoplasm  of  the 
nervous  tissue.  It  was  by  this  method  discovered  that  the 
nervous  system  was  made  up  of  a  multitude  of  units  or  neu- 
rones, which  are  perfectly  independent  anatomically  and  physio- 
logically of  each  other. 

Golgi's  Rapid  Method. — Harden  small  specimens  (i  to 
ijs  cm.)  of  young",  fresh,  nervous  tissue  in  ten  or  more 
volumes  of  three  per  cent,  bichromate  of  potash  solution  4 
parts,  one  per  cent,  osmic  acid  solution  i  part,  in  the  dark 
for  from  two  to  eight  days,  depending  upon  what  particular 
part  of  the  nervous  tissue  you  desire  to  impregnate.  For  neu- 
roglia it  must  remain  from  two  to  three  days ;  for  nerve-cells, 
three  to  five  days  ;  for  nerve-fibers,  five  to  seven  days. 

The  specimen,  after  having  hardened,  should  be  washed  in 
three-fourths  of  one  per  cent,  solution  of  silver  nitrate  and  then 
placed  for  one  or  two  days  in  one  per  cent,  solution  of  silver 
nitrate.  The  section  is  next  dehydrated  for  thirty  minutes  in 
ninety-six  per  cent,  alcohol,  and  then  cut  without  embedding  be- 
tween hardened  liver,  or  by  dipping  it  into  thick  celloidin  and 
fastening  it  to  a  block,  which  is  placed  in  chloroform  to  secure 
immediate  hardening  of  the  celloidin.  The  sections,  not  cut  too 
thin,  are  dehydrated  in  absolute  alcohol  for  a  short  time  and 
cleared  in  cedar,  clove,  or  bero-amot  oil,  and  mounted  in  Canada 
balsam  with  or  without  cover-slip. 

Golgi's  Slow  Method. — Small  cubes  of  fresh  nervous  tissue 
are  placed  in  a  recently  prepared  two  per  cent,  solution  of  bi- 
chromate of  potassium  at  room  temperature  for  two  to  six 
weeks,  or  until  sufficiently  hard.  They  are  then  placed  in  0.75 
per  cent,  solution  of  silver  nitrate  for  from  one  to  four  days,  or 
in  0.5  per  cent,  solution  of  corrosive  sublimate  for  two  or  three 
weeks.     Proceed  as  in  rapid  method. 

Berkley's  Method  of  Impregnation. — The  brain  or  cord 
is  hardened  in  Miiller's  fluid  until  it  is  sufficiently  hard  to  admit 


EXAMINATION  OF  THE  BRAIN  AND  SPINAL  CORD— TECHNIC.         567 

of  thin  sections  not  more  than  three  mm.  in  thickness.  These  are 
immersed  in  a  mixture  of  a  three  per  cent,  solution  of  potassium 
bichromate  and  one  per  cent,  osmic  acid,  in  the  proportion  of 
one  hundred  parts  of  the  former  to  twenty  of  the  latter.  In  this 
mixture  the  pieces  remain  for  three  or  five  days  ;  they  are  then 
removed  from  the  fluid,  dried  slightly  on  filter-paper  to  remove 
any  superfluous  bichromate.  They  are  next  washed  for  a  few 
minutes  in  a  weak  solution  of  silver  nitrate,  and  then  are  placed 
into  the  staining  mixture,  which  consists  of  two  drops  often  per 
cent,  solution  of  phosphomolybdic  acid  to  each  sixty  cubic  centi- 
meters of  a  one  per  cent,  solution  of  silver  nitrate  in  distilled 
water.  This  mixture  should  be  made  fresh  each  time.  Speci- 
mens remain  in  this  solution  from  three  to  five  days.  Cut  and 
mount  as  for  Golgi  specimens. 

Cox's  Modification  of  the  Golgi  Sublimate  Method. — 
This  method,  because  of  its  simplicity,  is  particularly  useful  for 
beginners.     It  stains  all  the  elements. 

A  small  tube  of  fresh  tissue  is  permitted  to  remain  for  six 
weeks  in  summer  and  for  three  weeks  in  winter  in  the  follow- 
ing mixture  : 

Five  per  cent,  solution  of  potassium  bichromate,  ...  20 

Five  per  cent,  solution  of  corrosive  sublimate,    ....  20 

Five  per  cent,  solution  of  potassium  chromate,     ...  16 

Aqua  destillata,  40 

Sections  are  cut  and  mounted,  as  in  the  Golgi  rapid  method. 
Tissue  previously  hardened  in  Miiller's  fluid  can  be  impreg- 
nated by  this  method.  Bevan  Lewis  has  recently  modified  this 
method  by  adding  to  the  sections  on  a  slide,  after  having  come 
out  of  alcohol,  a  few  drops  of  liquor  potassse  and  immediately 
washing  off  with  a  litde  distilled  water.  The  addition  of  the 
liquor  potassse  has  the  effect  of  bringing  out  the  elements  with 
intense  blackness. 

Weigert's  Method  of  Staining  the  Myelin  Sheaths. — 
To  Weigert  is  due  the  credit  of  discovering  a  unique  method  of 
staining  the  myelin  sheaths,  which  has  become  classic.  It 
depends  upon  the  fixation  of  the  myelin  with  chrome  salts  so 
that  it  can  not  be  dissolved  by  alcohol   or  ether,  and  acts  as 


S68  CENTRAL  NERVOUS  SYSTEM. 

a  distinct  mordant,  permitting   the  myelin   to  stain  very  deeply 
with  hematoxylin. 

1.  Harden  the  tissue  in  IMuller's  or  Krlitzky's  lluid. 

2.  Transfer  specimens  from  hardening  Huid  immediately  into 
ninety-six  per  cent,  alcohol ;    then  embed  in  celloidin. 

3.  Sections  should  be  cut  very  thin  and  placed  into  equal 
parts  of  water  and  a  saturated  neutral  solution  of  copper  acetate 
for  twenty-four  hours.'-' 

4.  Stain  for  from  thirty  minutes  to  twenty-four  hours  in  the 
following  solution  of  hematoxylin  : 

Hematoxylin  (Gruber's  or  Merck's), i 

Alcohol  absolute, 10 

Lithium  carbonate, i 

Aqua  destillata, ad  100 

5.  Wash  in  water  and  differentiate  for  a  few  minutes  to  half 
hour  in — 

Borax, 2 

Potassium  ferricyanid, 2.5 

Aqua  destillata loo 

6.  Wash  immediately  in  water,  dehydrate  in  alcohol,  clear  in 
xylol  or  origanum  oil,  and  mount  in  Canada  balsam. 

Of  the  many  modifications  of  Weigert's  original  method,  the 
one  devised  by  Pal  is  most  generally  used  and  gives  very  satis- 
factory results  : 

1.  Harden  specimens  as  for  Weigert's  method. 

2.  Place  section  for  overnight  in  three  per  cent,  solution 
potassium  bichromate,  or  for  several  hours  in  a  one-half  per 
cent,  solution  of  chromic  acid. 

3.  Stain  sections  in  Weigert's  hematoxylin  for  twenty-four  to 
forty-eight  hours. 

4.  Wash  in  water  plus  four  per  cent,  of  a  saturated  solution 
of  lithium  carbonate,  until  sections  appear  of  a  uniform  deep-blue 
color. 


*  Weigert  now  recommends  instead  of  this  solution  : 

Copper  acetate, 5 

Acetic  acid,  36  per  cent,  solution 5 

Chrome  alum, 2.5 

Water, ad  100  M. 


EXAMINATION  OF  THE  BRAIN  AND  SPINAL  CORD— TECHNIC.        569 

5.  Differentiate  in  a  freslily  prepared  one-third  per  cent,  solu- 
tion of  potassium  permang-anate  until  gray  matter  appears 
yellowish  brown,  about  half  a  minute. 

6.  Continue  differentiation  in  the  following  solution  until  the 
gray  matter  appears  white  and  the  white  matter  is  of  a  dark- 
blue  color : 

Oxalic  acid, I 

Potassium  sulphite, i 

Distilled  water,      200 

If  sections  do  not  differentiate  quickly,  transfer  them  again  to 
permanganate  solution  for  a  few  seconds  and  then  repeat  step  6. 

7;  Wash  thoroughly  in  water,  dehydrate  in  ninety-five  per 
cent,  alcohol,  clear  in  xylol  or  origanum  oil,  and  mount  in  Can- 
ada balsam. 

Erlitzky's  Fluid. 

Potassium  bichromate, 25 

Cuprum  sulphate, -5 

Aqua, loo.o 

Specimens  harden  at  room  temperature  in  from  ten  to  four- 
teen days, 

Marchi's  Method. —  i.  Fix  small  pieces  (2-3  mm.)  of  ner- 
vous tissue  for  eight  to  fourteen  days  in  Miiller's  fluid. 

2.  Transfer  to  a  mixture  composed  of  equal  parts  of  Miiller's 
fluid  and  one  per  cent,  solution  of  osmic  acid  for  six  to  twelve 
days. 

3.  Wash  in  running  water  for  twenty-four  hours. 

4.  Harden  in  alcohol,  embed  in  celloidin,  cut,  and  mount  in 
Canada  balsam  containing^  no  chloroform. 

This  method  is  very  useful  in  studying  secondary  degenera- 
tions. 

NEUROGLIA    STAINS. 

Differential  Stain  for  Neuroglia  Fibers. — Method  of 
Mallory. — i.  Fix  very  fresh  human  nervous  tissue  in  a  four  per 
cent,  aqueous  solution  of  formaldehyd  for  four  or  more  days. 

2.  Place  in  a  saturated  aqueous  solution  of  picric  acid  four  to 
eight  days. 

3,  Transfer  to  a  ffve  percent,  aqueous  solution  of  bichromate 


S70  CENTRAL  NERVOUS  SYSTEM. 

of  ammonia  lor  four  to  six  days  in  the  inculjator  at  2)7°  C.,  or  for 
three  to  four  weeks  at  room  temperature  ;  change  solution  on 
the  second  day. 

4.  Place  directly  into  alcohol. 

5.  Embed  in  celloidin. 

6.  Fasten  sections  to  slide  by  means  of  ether  vapor. 

7.  Stain  in  anilin-gentian  violet  fifteen  to  twenty  minutes. 

8.  Wash  off  with  normal  salt  solution. 

9.  lodin  solution  i  :  2  :  100  for  one  minute,  or  a  stronger 
solution  for  a  few  seconds. 

10.  Wash  thoroughly  with  water. 
I  I.   Dry  with  filter-paper, 

12.  Decolorize  in  equal  parts  of  anilin  oil  and  xylol. 

13.  Wash  off  thoroughly  with  xylol. 

14.  Mount  in  xylol  balsam. 

The  neuroglia,  nuclei,  and  to  some  extent  red  blood-corpuscles 
are  stained  blue.     The  other  tissue  elements  are  colorless. 

Mallorys  Phosphottino^stic-acid  Hematoxylin  MetJiod  for 
Staining  Neuroglia. —  i.  Fix  in  four  per  cent,  aqueous  solution 
of  formaldehyd  four  days. 

2.  Saturated  aqueous  solution  of  [)icric  acid  four  days. 

3.  Five  per  cent,  aqueous  solution  of  bichromate  of  am- 
monium four  days  to  six  days  in  incubator,  or  three  or  four 
weeks  at  room  temperature. 

4.  Stain  sections  in  phosphotungstic-acid  hematoxylin  four  to 
twenty-four  hours. 

5.  Wash  in  water. 

6.  Alcohol. 

7.  Clear  in  oleum  origani  cretici. 

8.  Mount  in  xylol  balsam. 

Neuroglia  fibers  and  nuclei  are  stained  blue,  connective  tissue 
deep  pink,  axis-cylinders  light  pink,  myelin  sheaths  yellow, 
protoplasm  of  ganglia  cells  and  dendrites  purplish  or  bluish 
gray.  Mallory  recommends  staining  sections  at  first  lightly  in 
Van  Gieson's  mixture,  which  stains  the  axis-cylinders  a  deep-red 
color. 


EXAMINATION  OF  THE  BRAIN  AND  SPINAL  CORD— TECHNIC.         571 

STAINS    FOR   AXIS-CYLINDER    PROCESSES. 

Neutral  carmin  is  an  excellent  stain  for  axis-cylinders,  also 
stains  nerve-cells  very  well.  Sections  should  remain  in  it  for 
twenty-four  hours,  when  they  should  be  thoroug-hly  washed  in 
water,  dehydrated  in  alcohol,  cleared  in  clove  oil,  and  mounted 
in  Canada  balsam.  To  prepare  neutral  carmin,  dissolve 
without  heat  one  gram  of  carmin  in  50  c.c.  of  aqua  destil- 
lata,  plus  5  c.c.  aqua  ammonia.  Expose  the  mixture  to  the 
air  until  no  ammonlacal  odor  exists  ;  filter,  and  keep  tightly 
corked. 

To  stain  axis-cylinders  with  nigrosin  proceed  as  follows  : 

1.  Stain  sections  for  five  or  ten  minutes  in  a  saturated  watery 
solution  of  nigrosin. 

2.  Decolorize  in  dilute  alcohol,  then  in  absolute  alcohol. 

3.  Clear  in  oil  of  origanum  ;   mount  in  Canada  balsam. 
This  very  simple   method  gives   beautiful   results.     It  stains 

well  the  ganglion  cells  and  their  protoplasmic  processes.     De- 
generated areas  are  stained  a  bluish  black. 

Van  Gieson's  Method. — i.  Specimens  should  be  hard- 
ened in  Miiller's  fluid  or  alcohol. 

2.  Stain  for  from  five  minutes  to  one-half  an  hour  in  alum 
hematoxylin. 

3.  Wash  thoroughly  in  water. 

4.  Stain  for  three  to  five  minutes  in  Van  Gieson's  solution, 
which  consists  of  one  percent,  aqueous  solution  of  acid  fuchsin, 
15  c.c.  saturated  aqueous  solution  of  picric  acid,  50  c.c.  aqua 
destillata. 

5.  Wash  in  water  for  a  short  time. 

6.  Dehydrate  in  alcohol ;  clear  in  clove  oil ;  mount  in  Canada 
balsam. 

The  axis-cylinders  and  ganglion  cells  are  deep  red,  myelin 
sheaths  yellow,  neuroglia  red,  nuclei  lilac. 


572  CENTRAL  NERVOUS  SYSTEM. 

STAINS    FOR    END    ORCiAXS,  TERMINATIONS    OF    NERVES,    AND 
('( )I. LATERAL    r.RANCHES. 

Method  of  Gerlach. —  i.  Tissue  should  be  hardened  in  one 
or  two  per  cent,  sohition  of  ammonium  bichromate  for  three 
weeks  ;  when  specimen  is  sufficiently  hard,  it  should  be  sectioned 
under  water  without  the  use  of  alcohol.  Put  sections  in  a  y|^ 
per  cent,  solution  of  chlorid  of  gold  and  potassium. 

2.  Acidulate  with  a  few  drops  of  hydrochloric  acid  for  twelve 
hours,  or  until  they  become  of  a  slight  violet  color. 

3.  Wash  in  a  very  weak  solution  of  hydrochloric  acid,  i  :  2000. 

4.  Put  sections  in  a  yV  per  cent,  solution  of  hydrochloric  acid, 
and  in  sixty  per  cent,  alcohol  for  ten  minutes. 

5.  Absolute  alcohol ;  clear  in  clove  oil  ;  mount  in  Canada 
balsam. 

Method  of  Freud. —  i.  Harden  specimens  at  first  in  Er- 
litzky's  or  MuUer's  lluid,  then  in  alcohol. 

2.  Embed  in  celloidin,  cut  sections  and  place  them  in  a  one 
per  cent,  solution  of  chlorid  of  gold  for  three  to  five  hours. 

3.  Wash  in  water  and  bring  sections  for  reduction  in  a  solu- 
tion composed  of  sodium  hydrate  i,  aqua  destillata  5,  for  three 
minutes. 

4.  Wash  in  water  and  place  sections  for  from  five  to  fifteen 
minutes  in  ten  per  cent,  solution  of  potassium  iodid,  until  sections 
appear  reddish  violet. 

5.  Wash  in  water,  dehydrate  in  alcohol,  clear  in  xylol,  and 
mount  in  Canada  balsam. 

Method  of  S.  Ramon  y  Cajal  to  show  the  collaterals. — 
I.  Rather  thin  sections  of  fresh  rabbit's  brain  are  brushed  over 
with  a  saturated  solution  of  methylene-blue  (B.  Gruber),  or 
methylene-blue  in  a  powder  is  dusted  over  the  sections  ;  after 
three-quarters  of  an  hour  the  sections  are  washed  in  weak  saline 
solution. 

2.   Fix  in  solution  of — 

Ammonium  molylxlate, lo 

Distilled  water,       too 

Hydrochloric  acid lo  drops 

for  two  or  three  hours. 


EXAMINATION  OF  THE  BRAIN  AND  SPINAL  CORD— TECHNIC.        573 

3.  Wash  in  water  to  remove  excess  of  ammonium  molyb- 
date,  and  harden  for  three  to  four  hours  in — 

Formalin, 40 

Distilled  water,      60 

One  per  cent,  solution  platinum  chlorid, 5 

4.  Wash  quickly  to  remove  the  formahn  for  several  minutes 
in  a  three  per  cent,  alcoholic  solution  of  platinum  chlorid. 
Embed  in  paraffin. 

5.  Thick  sections  are  dehydrated  in  alcohol  absolute  with  the 
addition  of  ]4,  V^^  cent,  platinum  chlorid;  clear  in  xylol;  mount 
in  Canada  balsam. 

Ehrlich's  Vital  Methylene-blue  Method  (Modified  by 
SemiMeyer). —  i.  Hypodermic  injection  of  methylene-blue  BX 
solution  (saturated  at  2)7°  C.),  2  c.c.  at  intervals  of  fifteen  to 
thirty  minutes.      Ready  after  three  to  six  injections. 

2.  Brain  to  be  cut  into  two  or  three  pieces  and  put  into  the 
following  solution  for  twenty-four  hours  at  a  temperature  of 
32°  F.: 

Ammonium  molybdate, lo 

Distilled  water loo 

Hydrochloric  acid,  cone, lo  drops. 

3.  Wash  in  running  water  for  two  hours, 

4.  Place  specimens  in  eighty  per  cent,  alcohol  for  one-half  to 
one  hour,  then  in  ninety-five  per  cent,  alcohol  for  same  length 
of  time,  and  then  into  several  changes  of  absolute  alcohol. 
All  No.  4  at  ice  temperature  (32°  F.). 

5.  Xylol  (several  times  to  be  renewed)  ;  embed  in  paraffin. 

6.  Cut,  clear  in  xylol,  and  mount  in  Canada  balsam. 


GENERAL    STAINS. 

Hematoxylin  is  the  most  useful  of  the  general  stains.  It 
stains  the  nuclei  and  connective  tissue,  and  stains  quite  well  the 
ganglion  cells  and  processes.  The  following  formulae  contain 
hematoxylin  as  the  base,  and  will  be  found  useful  in  staining 
nervous  tissue  : 

Phosphomolybdic-acid  Hematoxylin  (Mallory). 

Hematoxylin  crystals, 1. 75  grams 

One-half  per  cent,  aqueous  solution  of  phosphomolybdic 

acid, 200  c.c. 


574  CENTRAL  NKRVOUS  SYSTEM. 

Expose  solution  to  light  in  a  bottle   plugged  with  absorbent 
cotton  ;  it  will  be  ready  for  use  in  six  weeks. 

1.  Stain  section  from  twenty  minutes  to  one  hour. 

2.  Wash  in  two  or  three  changes  of  fifty  per  cent,  alcohol  until 
celloidin  becomes  completely  decolorized. 

3.  Dehydrate  in  ninety-five  per  cent,  alcohol,  clear  in  clove  oil, 
and  mount  in  balsam. 

Khki.ich's  Acid  Hematoxylin. 

Hematoxylin  crystals, 2  grams. 

Alcohol,  absolute,  ...         60  c.c. 

Acetic  acid  (glaciall, 3  c.c.    1                    ,  ■  , 

,,,  ^  Saturaied  with 

Water,                                                  .                             .    .  60  c.c.     y  , 

1  ammonia  alum. 


Glycerin, 60 


c.c. 


This  solution  is  exposed  to  the  light  for  three  weeks,  when  it 
is  ready  for  use.  Specimens  are  stained  for  a  few  minutes, 
washed  in  water,  dehydrated  in  alcohol,  cleared  in  xylol  or  oil, 
and  mounted  in  Canada  balsam. 

Aqueous  Alu.m  He.\i.\toxvi.in  Solution. 

Hetnato.xylin  crystals, I 

Saturated  aqueous  solution  of  ammonia  alum,    ....  loO 

Water, 300 

Thymol,       a  few  crystals. 

The  solution  should  be  exposed  to  the  light  for  about  two 
weeks,  when  it  is  ready  for  use.  The  author  prefers  this  solu- 
tion to  Delafield's.  Excellent  contrast  stains  are  eosin  and 
anilin  blue-black ;  the  latter  stains  the  axis-cylinders  and  proto- 
plasmic processes. 

Stain  with  alum  hematoxylin  for  a  few  minutes,  then  place 
sections  in  watery  solution  of  eosin  until  sections  are  stained 
red,  wash  in  water,  dehydrate  quickly  in  alcohol,  clear  in  clove 
oil,  and  mount  in  Canada  balsam. 

Stain  with  alum  hematoxylin  for  a  few  minutes,  then  place 
sections  direct  in  a  five  per  cent,  watery  solution  of  anilin  blue- 
black  for  a  few  seconds,  wash,  clear,  and  mount  as  above.  The 
nerve-cells  are  stained  bluish,  while  the  neuroglia  cells  are 
stained  a  lilac. 


INDEX. 


Abducens  nerve,  l66 
Accessory  nucleus,  76,  1S5 
Acervulus  cerebri,  247 
Acoustic  nucleus,  anterior,  173 
ventral,  172 
Acousticocerebellar  tract,  166,  177,  207 
Adventitial  lymph-space,  58,  63 
Agraphia,  472 
Ala  cinerea,  135 
Alexia,  470 

Alternate  hemiplegia,  490 
Alveus,  318,  354,  356,  394 
Amacrine  cells,  265 
Amnesic  aphasia,  468 
Amygdaloid  nucleus,  399 
Amygdalum,  190 
Amyotrophic  lateral  sclerosis,  501 
Anastomotic  vein,  great,  439 

posterior,  439 
Angular  gyrus,  308 
Ansa  lenticularis,  402 
Anterior  cerebral  artery,  422 
choroid  artery,  424 
commissure  of  spinal  cord,  74 
communicating  artery,  421 
inferior  cerebellar  arteries,  431 
Anterolateral  arteries,  423 
Aphasia,  amnesic,  468 
motor,  472 
of  conduction,  486 
tactile,  471 
verbal,  468 
Apices  cornuum  posteriores,  74 
Aqueduct  of  Sylvius,  210 

development  of,  530 
Sylvian,  132 
Arachnoid,  cerebral,  284 
spinal,  65 
villi,  287 
Arantius,  ventricle  of,  135,  136 
Arborization,  200 
Arborizations,  interepithelial,  38 
Arcuate  fibers,  164 

anterior  external,  204 
antero-external,  165 
external,  204 
internal,  144 
"posteroexternal,  165 


Area  of  Broca,  335 

posterior,  of  medulla,  126 
Areas,  lateral,  of  medulla,  126 
Arkyostichochrome  nerve-cells,  21 
Arm- area  of  cerebral  cortex,  451,  452 
Arnold,  substantia  reticularis  of,  355 
Arterial  supply  of  cerebrum,  417 

to  medulla  oblongata,  432 
to  pons  Varolii,  432 
Arteries,  anterior  inferior  cerebellar,  431 
anterolateral,  423 
carotid,  418 
inferior  cerebellar,  431 
lenticulo-optic,  424 
lenticulostriate,  424 
long,  of  brain,  416 
middle  cerebellar,  431 
of  brain  and  cord,  58 
of  cerebral  dura  mater,  283 
posterior  cerebral,  425 
^  superior  cerebellar,  430 
vertebral,  425 
Artery,    anterior  cerebral,  421 
choroid,  424 
communicating,  421 
ascending  frontal,  422 

parietal,   422 
basilar,  425 
inferior  frontal,  422 
internal  auditory,  425 
marginofrontal,  421 
middle  cerebral,  422 
of  cerebral  hemorrhage,  424 
parietotemporal,  423 
posterior  communicating,  424 

meningeal,  425 
quadrate,  421 
sphenoid,  423 
Sylvian,  422 
Articular  end  bulbs,  40 
Ascending  frontal  artery,  422 
parietal  artery,  422 
Association,    centers    of,    of    cerebral    cortex, 

507 
fibers  of  centrum  ovale,  364 
zones  of,  of  cerebral  cortex,  507 

Astrocytes,  56 

Ataxic  paraplegia,  503 

Atrophy,  progressive  muscular,  501 


575 


576 


INDKX. 


Auditory  artery,  internal,  425 
centers,  462 
nerve,   171 

connections  of,  175 
dorsomesial  nucleus  of,  174 
nuc'eus,  anterior,  173 

dorsolateral,  174 
dorsomesial,  174 
sphere  of  cerebral  cortex,  507 
Axilemma,  34 
Axioplasm,  ^2 
Axis-cylinder,  31 

nigrosin  for  staining,  571 
of  Turk  in  je,  32 
process,  47,  49 
processes,  stains  for,  571 
Axone,  3I,  47,  49 


Back-muscles,  nucleus  for,  79 
Baillarger,  outer  line  of,  339 
Basal  ganglia,  lesions  of,  48S 
Basilar  artery,  425 
sinus,  444 
vein,  437 
Basket  cell  of  cerebellum,  28 

cells,  199 
Becliterew    and    Flechsig,    central    tegmental 
tract  of,  152 
nucleus  of,  175,  1S2 
olivary  tract  of,  I05 
Berkley's  method  of  impregnation,  566 
Bipolar  nerve-cells,  24 
Blood-supply  of  spinal  cord,  122 
Blood-vessels,  cortical,  416 
of  brain,  416 

of  central  nervous  system,  58 
of  cerebellum,  430      , 
Bodenplatte,  525 
Bodies,  olivary,  126 

restiform,   164 
Body,  Luys',  259,  260 
Nissl,  18 
]>ituitary,  276 
Bogenfurche  of  His,  542 
Boundary  zone,  1 14 
Brachia  conjunctiva,  202 
Brachial  enlargement  of  spinal  cord,  69 
Brain,  blood-vt-ssels  of,  416 
central  vessels  of,  416 
ganglionic  vessels  of,  416 
long  arteries  of,  416 
membranes  of,  280 
motor  area  of,  449 
technic  of  microscopic  and  macroscopic 

examination  of,  559 
venous  systems  of,  435 
Brain-sand,  247 
Broca,  area  of,  335,  471 

space  of,  335 
Brown-Sequard's  paralysis,  504 
Buds,  200 
Bulb,  69,  125 

of  internal  jugular  vein,  445 
olfactory,  319,  328 

fourth  layer  of,  332 


Bulb,  olfactoiT,  large  mitral  cells  of,  330 

layer   of    central    nerve-fibers 

of,  332 
molecular  layer  of,  330 
outer  layer  of,  328 
pyramidal  cells  of.  330 
superficial    layer    of    medium 
and  small -sized  cells  of,  33 1 
Bulbar  paralysis,  acute,  499 
Bundle,  conmia-shaped,  99 
hcmispheral,  337 
inferior  longitudinal,  368 
Meynert's,  257 
of  gyrus  fornicatus,  364 
of  Vicq  d'Azyr,  253,  324,  413 
posterior,  337 

longitudinal,  82 

nucleus  of,  230 
su]ierior  longitudinal,  230 
triangular,  105 
Burdach,  column  of,  84,  91,  99,  126 
nucleus  of,  144 
fasciculus  arcuatus  of,  368 
Buschzellen,  254 


Cajal  cells,  50-52.  343 

varieties  of,  344 
commissural  nucleus  of,  158 
method  of  staining,  572 
Calamus  scripturius,  132,  136 
Calcar  avis,  300,  397 
Ca^carine  fissure,  3C0 
Callo-omarginal  fissure,  303,  545 
Canal,  central,  of  spinal  cord,  74,  1 22 

neural,  508 
Capillaries  of  nervous  system,  60 
Caps,  nuclear,  18 
Capsule,  internal,  399,  407 

localization    of    lesions    of, 
488 
Caput  cornu,  72 
Carmin,    neutral,    for    staining    axis-cylinders 

and  nerve  cells,  571 
Carotid  arteries,  418 
Cauda  equina,  69 
Caudate  nucleus,  399 
Cavernous  sinuses,  446 
Cavuni  Meckelii,  2S0 
Cell-bodies,  47 

Cell -group  for  upper  extremity,  79 
Cell -processes,  30 
Center  for  ideas,  467 

reception  of  appearance  of  objects 
gained  through   sense 
of  touch,  470 
of  heard  words,  466 
of  memories    for  appear- 
ance of  objects    seen 
and  of  words  written 
or  printed,  469 
of      muscular     memories 
necessary    to     produce 
speech,  471 
retraction  of  angle  of  mouth,  453 


INDEX. 


577 


Center  for  smell,  483 
for  taste,  482 
for  writing,  sensory,  479 
half-vision,  461 
olfactory,  483 
Centers,  auditory,  462 

cortical,  for  general  sensations,  454 

for  writing,  475 
for  language,  465 

of  association  of  cerebral  cortex,  507 
of  vision,  457 

which  preside  over  higher  intellectual 
faculties,  480 
Central  canal  of  spinal  cord,  74,  122 
convolutions,  307 

anterior,  305 
gyrus,  posterior,  306 
sulcus,  310 
vessels  of  brain,  416 
Centrum  ovale,  association  fibers  of,  364 

localization  of  lesions  in,  484 
minute  anatomy  of,  338,  362 
of    parietal    lobe,    lesions    of, 
486 
semiovale,  lesions  of,  beneath  motor 
area,  485 
of  occipital  lobe,  487 
of  temporal  lobe,  lesions 
of,  486 
Cerebellar  arteries,  inferior,  431 
middle,  431 
superior,  430 
commissures,  207 

hemisphere,  lobules  of  inferior  sur- 
face of,  190 
lobules  of   superior  or 
dorsal  surface  of,  190 
hemispheres,  lesions  of,  494 

tract     connecting     oc- 
cipital and  temporal 
lobes  with,  221 
lesions,  localization  of,  493 
peduncle,  inferior,  182,  203 

middle,  lesions  of,  495 
peduncles,  202 

middle,  203 
superior,  202,  229 
tract,  anterolateral  descending,  104 
descending,  204 
direct,  90,  95,  143,  204 
sensory,  166,  177J 
tracts,  direct-,  203 

sensory,  207 
veins,  inferior,  441 
superior,  440 
Cerebello-olivary  tract,  160,  164,  207 
Cerebellum,  186 

anterior  commissure  of,  207 
basket  cell  of,  28 
blood-vessels  of,  430 
connections  of,  187 

of    vestibular    nerve 
with,  176 
cortex  of,  198 
development  of  528 
inferior  peduncles  of,  188 

37 


Cerebellum,  inferior  vermiform     process     of, 
186 
lesions  of  middle  lobe  of,  493 

of  worm  of,  493 
middle  lobe  of,  1S6 

peduncles  of,  188 
minute  anatomy  of,  193 
peduncles  of,  188 
posterior  commissure  of,  208 
superior  peduncles  of,  1 88 
upper  surface  of,  187 
veins  of,  440 

vermiform  process  of,  186 
worm  of,  186,  188 
Cerebral  arachnoid,  284 

arteries,  posterior,  425 
artery,  anterior,  421 
middle,  422 

central    branches    of, 

423 
ganglionic     branches 
of,  423 
cortex,  auditory  sphere  of,  507 

centers  of  association  of,   507 
connection  of  optic  thalamus 

with,  251 
divisions     of,     according     to 

Flechsig,  506 
histology  of,  ^^8 
layers  of,  338 
olfactory  sphere  of,  507 
projection  spheres  of,  507 
sensory  spheres  of,  507 
stratum  zonale  of,  338 
tangential  fibers  of,  339 
visual  sphere  of,  507 
zones  of  association  of,  507 
dura  mater,  280 

hemisphere, development  of  commis- 
sural system  of,  543 
evolution  of  fissures  of, 

545 
primary  fissures  of,  545 
secondary  fissures  of,  545 
hemispheres,  base  of ,  318 

development  of,  538 
general  anatomy  of  in- 
terior of,  387 
hemorrhage,  artery  of,  424 
localization,  448 
peduncles,  220 
pia  mater,  288 
vein,  anterior,  437 
middle,  437 
veins,  435 

deep,  440 
superficial,  436 
vesicles,  primary,  508 

secondary,  511  ' 

Cerebrospinal  fluid,  286 
Cerebrum,  293 

anterior  commissure  of,  336 
arterial  supply  of,  417 
central  fissure  of,  299 
choroid  fissure  of,  297 
convolutions  of,  ^o^ 


578 


INDEX. 


Cerel 'rum,  convolutions  of  mesial    surface  of, 

315 
fissures  of,  294 

of  external  surface  of,  294 
gyri  of,  303 
inferior      longitudinnl     fissure     of, 

lobules  of,  303 

longitudinal  fissure  of,  293,  294 
peduncles  of,  325 
secondary  fissures  of,  294 
transverse  fissure  of,  294 
Cervical  enlargement  of  spinal  cord,  69 

region  of  spinal  cord,  1 17 
Cervix  cornu,  72 

Charcot,  posterior  root-zone  of,  91 
Chiasm,  optic,  274 

development  of,  539 
Choroid  artery,  anterior,  424 
fissure  of,  542 

of  cerebrum,  297 
plexuses,  288 

of  fourth  ventricle,  291 
vein,  440 
Chromophyllic  granules,  18 
Chromoplasm,  17 

Ciaglinski,  long  sensory  tract  of,  106 
Cingulum,  364 
Circle  of  Willis,  429 
Circular  sinus,  444 

Cisterna  magna  cerebellomedullaris,  285 
Clarke,  Lockhart,  vesicular  column  of,  83 
Claustrum,  407 
Clava,  131 
Cochlear  nerve,  171 
Collateral  branches,  stains  for,  572 

fissure,  547 
Collaterals,  50 
Color-vision,  462 
Column,  anterior,   of  spinal  cord,  84 

lateral,     connections     of     vestibular 

nerve  with,  177 
of  Burdach,  84,  91,  99,  126 
nucleus  of,  144 
of  Flechsig,  83,  90,  143,  203 
of  Goll,  84,  91,  99,  126 

nucleus  of,  131,  144 
of  Lissauer,  114 

posterointernal,  of  spinal  cord,  9I 
vesicular,  83 
Columns,  anterior,  of  medulla,  126 

lateral,  ground  bundles  of,  107 
nuclei  of,  I43 
of  medulla,  126 
of  spinal  cord,  84 
of  Tiirck,  89 

posterior,  course  of  fibers  of,  97 
of  spinal  cord,  84 
Comma-shaped  bundle,  99 

fasciculus,  114 
Commissural  cells  of  spinal  cord,  83 
nucleus  of  Cajal,  158 
svstem    of    cerebral    hemisphere, 
development  of,  543 
Commissure,  anterior,  372,  400 

of  cerebellum,  207 


Commissure,  anterior,  of  cerebrum,  336 
of  spinal  cord,  74 
gray,  of  spinal  cord,  74,  75 
inferior,  of  Gudden,  275 
Meynert's,  276 

middle,  of  third  ventricle,  245 
posterior,  of  cerebellum,  208 
of  pineal  gland,  248 
of  spinal  cord,  74,  75  « 
soft,  of  third  ventricle,  245 
white,  of  spinal  cord,  74 
Commissures,  cerebellar,  207 

of  spinal  cord,  71 
Communicating  artery,  anterior,  421 

posterior,  424 
Conarium,  246 
Conduction,  aphasia  of,  486 
Conus  medullaris,  69 
terniinalis,  115 
Convolution,  anterior  central,  305 
first  temporal,  313 
inferior  parietal,  308 

temporal,  314 
marginal,  315 
middle  temporal,  314 
of  corpus  callosuni,  316 
second  temporal,  314 
superior  temporal,  313 
third  temporal,  314 
Convolutions,  central,  30-7 
motor,  307 
occipital,  309 
of  cerebrum,  303 
of  mesial   surface  of  cerebrum, 

315 
superior  parietal,  307 
temporoparietal,  310 
veins  of,  438 
Cord,  central  ligament  of,  69 
dorsal,  69 
spinal,  64 
Cornu  ammonis,  353,394 

anatomy  of,  350 
commissural  tract,  loo,  loi 
Cornua,  anterior,  of  spinal  cord,  72 
of  lateral  ventricle,  393 
of  spinal  cord,  72 
Corpora  albicantia,  324 

development  of,  536 
mammillaria,  324 

development  of,  536 
quadrigemina,  210 

development  of,  530 
lesions  of,  488 
restiformia,  188,  203 
striata,  398 
trapezoidea.  175,  1 80 
Corpus  callosum,  293,  319,  371,  387 
convolution  of,  316 
genu  (if,  414 
lesions  of,  487 
peduncles  of,  388 
ventricle  of,  393 
ciliare,  194 
dentatum,  194 
fimbriatum,  394 


INDEX. 


579 


Corpus  striatum,  vein  of,  440 

trapezoideus,  194 
Corpuscles  of  Golgi,  43 
Pacinian,  41 
tactile,  39 
Vater's,  41 
Cortex,  cerebral,  auditory  sphere  of,  507 

centers  of  association  of,  507 
divisions    of,    according    to 

Flechsig,  506 
histology  of,  338 
layers  of,  ^^^ 
olfactory  sphere  of,  507 
projection  spheres  of,  507 
sensory  spheres  of,  507 
tangential  fibers  of,  339 
visual  sphere  of,  507 
zones  of  association  of,  507 
of  cerebellum,    198 
pyramidal  cells  of,  2S 
stratum  zonale  of,  338 
Cortical  area  for  muscles  of  trunk  and  spine, 
453 
governing  motion,  449 
blood-vessels,  416 
cells,  layers  of,  343 
center  for  general  sensations,  454 
for  smell,  483 
for  taste,  482 
for  writing,  475 
fibers,  layers  of,  343 
layer,  molecular,  343 
outer,  343 
superficial,  343 
Cox's   modification   of    the    Golgi   sublimate 

method  of  staining,  567 
Cranial  nerve,  fifth,  superior  or  accessory  nu- 
cleus of,  240 
nerves,  development  of,  547 
eleventh  pair  of,  139 
fourth  pair  of,  240 
sensory  fibers  of,  547 
third  pair  of,  235 
twelfth  pair  of,  nuclei  of  origin 
of,  151 
Crossed  paralysis,  490 
Crosses  of  Frohmann,  34 
Cross-legged  progression,  500 
Crura  cerebri,  325 

development  of,  530 
lesions  of,  489 
Crusta,  220,  325 
Culmen,   189 
Cuneate  lobule,  190 
Cuneus,  316  " 

Cup,  optic,  552 
Cytochrome  nerve-cells,  22 


Decussation,  pyramidal,  140 
sensory,  144 
superior  sensory,  224 
Degeneration,  secondary,  87 
Deiter,  large-celled  nucleus  of,  174 
nucleus  of,  182 
protoplasmic  processes  of,  47 
spider-cells  of,  56 
Dejerine's  method  of  sectioning  brain,  560 
Dendrites,  47,  48 

function  of,  48 
number  of,  48 
Dentate  gyrus,  318 

ligament,  66 
Diaphragma  sellse,  283 
Diencephalon,  511 
Digastric  lobule,  190 
Dorsal  cord,  69 

funiculi,  course  of  fibers  of,  97 
region  of  spinal  cord,  116 
Doyere,  eminences  of,  45 
Dura,  64 

mater,  cerebral,  2S0 

arteries  of,  283 
nerve-supply  of,  284 
processes  of,  281 


E. 

Edinger,  tegmental  radiation  of,  403 

Edinger's  nucleus,  230 

Ehrlich's    vital    methylene-blue     method     of 

staining,  573 
Eleventh  pair  of  cranial  nerves,  139 
Embryology  of  central  nervous  system,  508 
Eminences  of  Doyere,  45 
Eminentia  cinerea,  135 

collateralis,  300,  394 
teres,  168 
Emissary  veins,  447 
End  bulbs,  articular,  40 

of  Krause,  40 
Endocranium,  280 
Endoneurium,  36 
End-organs,  stains  for,  572 
Enlargement,  brachial,  of  spinal  cord,  69 
cervical,  of  spinal  cord,  69 
lumbar,  of  spinal  cord,  69 
Epencephalon,  186 
Ependyma,  135,  354,  393 
Epidural  space,  64 
Epineurium,  36 
Epiphysis  cerebri,  246 
Erb's^palsy,  500 
Eyelids,  elevation  of,  center  for,  453 


D. 

Deckplatte,  525 

Declive,   189 

Decussation,  interolivary,  144,  224 

motor,  140 

optic,  320 

posterior  pyramidal,  144 


Face-area  of  cerebral  cortex,  451,  452 
Facial  nerve,  168 

connections  of,  171 
Falciform  lobe,  317 

sinus,  442 

vein,  443 
Falx  cerebelli,  282 


5So 


INDEX. 


Falx  cerebri,  2S1 
Fascia  dentata,  318,  359 
Fasciculi  cerebrospinalis  lateralis,  90 
garland-like,  20S 
tereles,  135 
Fasciculus  arcuatus,  364,  368 
cerebellospinalis,  75 
inferior  longitudinal,  39 
occipitofrontalis,  369 
olivary,  105 
perpendicular,  370 
retroflexus,  257 
superior  longitudinal,  368 
thalamomauimillaris,  253,  413 
uncinatus,  368 

ventrolateralis  superficialis,  103 
Fasciola  cinerea,  318 
Fibers,  projection-system  of,  373 
Fibne  arcuatci;  propria,  364 
Fibrillin,  primitive,  ^^ 
Fields  of  innervation,  45 

P'ifth    cranial    nerve,    superior    or    accessory 
nucleus  of,  240 
ventricle,  414 
Fila  olfactoria,  326 

Fillet,  internal  or  mesial,  connections  of  vesti- 
bular nerve  with,  177 
lateral,  18 1,  228 

connections  of  vestibular  nerve 
with,  177 
mesial,  144,  180,  223 
Filum  terminale,  69, 92 
Fimbria,  318,  394 
Fissure,  anterior  longitudinal,  of  spinal  cord, 

calcarine,   300 
callosomarginal,  303,  545 
central,  of  cerebrum,  299 
choroid,  542 

of  cerebrum,  297 
collateral,  547 

dorsal,  of  spinal  cord,  71,72 
inferior  longitudinal,  of  cerebrum,  319 
interparietal,  300,546 
intraparietal,  300,  546 
lateral,  300 

longitudinal,  of  cerebrum,  293.  294 
occipital,  299 
occipitotemporal,  547 
of  Rolando,  299,  545 
of  Sylvius,  298 

development  of,  540 
parietooccipital,  299 
posterior  longitudinal,  of  spinal   cord, 

of  spinal  cord,  72 
postero-inteniiediate,    of  spinal    cord, 

72 
precentral,  546 
prepyramidal,  190 
primar}-,  542 
Sylvian,  320 

transverse,  of  cerebrum,  294 
ventral,  of  spinal  cord,  71 
Fissures  of  cerebral  hemisphere,  evolution  of, 
545 


Fissures  of  cerebram,  294 

of  external  surface  of  cerebrum,  294 
of  frontal  lobe,  546 
of  island  of  Reil,  546 
of  occipital  lobe,  546 
of  parietal  lobe,  546 
of  temporal  lobe,  546 
primary,  of  cerebral  lu-misphcre,  545 
secondary,  of  cerebral  hemisphere,  545 
of  cerebrum,  294 
Flechsig,  anterior  ground-bundles  of,  90 
columns  of,  83,  90,  143,  203 
nucleus  vestibularis  of,  175 
posterior  ground-bundle  of,  9I 
Fleece,  197 
Flocculus,  190 
Fluid,  cerebrospinal,  2S6 
Folds,  medullary,  508 
Foramen  ca.'cum,  125 

of  Magendie,  132,  285 
of  Monro,  246 
Foramina  of  Key  and  Retzius,  2S5 
Forceps  major,  393 
minor,  390 
posterioris,  397 
P"ore-brain,  293 
Formatio  reticularis,  146,  180 

alba,  148,  180 
grisea,  146,  180 
Fornix,  249,  373,  413 
Fossa  of  Sylvius,  development  of,  540 

Sylvii,  298 
Fourth  pair  of  cranial  nerves,  240 
Fovea  inferior,  135 
superior,  135 
Fraenulum  lingulse,  189 
Freud,  method  of  staining  of,  572 
Frohmann,  crosses  of,  34 

lines  of,  33 
Frontal  artery,  ascending,  422 
inferior,  422 
gjTus,  ascending,  305 
first,  303 
inferior,  304 
middle,  304 
second, 304 

inferior  part    of  dorsal 
portion  of,  304 
superior,  303 
third,  304 
lobe,  303 

fissures  of,  546 
Frontocerebellar  tract,  222,  353 
Funiculi,  dorsal,  course  of  fibers  of,  97 

teretes,  135 
Fuss,  220 


Galen,  veins  of,  440 
Ganglia,  basal,  lesions  of,  4S8 

of  sensory  cranial  nerves,  548 
spinal,  109 
Ganglion  cell,  17 

habenuh^j,  249,  257 
interpeduncular,  258 


INDEX. 


581 


Ganglion,  spinal,  posterior,  71 
Ganglionic  cells  of  retina,  264 

vessels  of  brain,  416 
Garland-like  fasciculi,  208 
Gemmules,  48,  200 
Geniculate  body,  external,  250 
internal,  250 
lateral,   250 
Genu  of  corpus  callosum,  414 
Gerlach,  method  of  staining  of,  572 
Giant  pyramidal  cells,  29 
Glands,  Pacchionian,  287 
Glia-cells,  56 
Globus  pallidus,  399 
Glomeruli,  olfactory,  layer  of,  329 
Glossopharyngeal  nerve,  155 

motornucleus  of,  158 
Golgi,  corpuscles  of,  43 

Golgi's   method  for  sta'ning  nerve-cells   and 
their  processes,  566 
rapid  method  of  staining,  566 
slow  method  of  staining,  566 
Goll,  column  of,  84,  91,  99,  126 

nucleus  of.  131,  144 
Gowers  and  Bechterew,    anterolateral  ascend- 
ing tract  of,  233 
anterolateral    ascending    tract    of,  80, 
90,  103 
Gowers'  tract,  385 
Granular  nerve-cells,  24 
Granules,  chromophyllic,  18 
of  Nissl,  18 
protoplasmic,  18 
Gray  commissure,  74,  75 

matter  of  spinal  cord,  71 

neuroglia  of,  12 1 
substance,  intermediate,  74 
Groove,  medullary,  508 

posterolateral,  of  spinal  cord,  72 
Ground  bundle  of  fibers,  lateral,  233 
posterior,  91 
bundles,  anterior,  107 

function  of,  107 
of  Flechsig,  90 
of  lateral  columns,  107,  234 
Gudden,  inferior  commissure  of,  275 
Gyri  of  cerebrum,  303 
Gyrochrome  nerve-cells,  22 
Gyrus,  angular,  308 

ascending  frontal,  305 
parietal,  306 
cinguli,  316 
dentatus,  359 

anatomy  of,  350 
first  frontal,  303 

occipital,  309 
fornicatus,  316 

bundle  of,  364 
hippocarapal,  350 
hippocampus,  317 
inferior  frontal,  304 

occipital,   309 
lingual,  300 
marginal,  315 
middle  frontal,  304 
occipital,  309 


Gyrus,   occipitotemporal,  middle,  300 
posterior  central,  306 
postparietal,  308 
rectus,  306 
second  frontal,  304 

occipital,  309 
superior  frontal,  303 

occipital,  309 
supramarginal ,  308 
third  frontal,  304 

occipital,  309 
uncinate,  ?i8 


H. 

Half-vision  center,  461 
Helweg,  triangular  bundle  of,  105 
Hematoxylin  as  a  general  stain,  573 
Hemiplegia,  alternate,  490 
Hemispheral  bundle,  337 

Hemisphere,  cerebral,  development    of   com- 
missural system    of, 

543. 
evolution    of     fissures 

of,  545 
primary  fissures  of,  545 
^  secondary    fissures  of, 

545 
Hemispheres,   cerebral,  base  of,  318 

development  of,  539 
general    anatomy     of 
interior  of,  387 
Hilum  of  olivary  body,  160 
Hippocampal  gyrus,  350 
Hippocampus  major,  394 

anatomy  of,  350 
minor,  300,  397 
His,  Bogenfurche  of,  542 

spaces  of,  58 
Horn  of  spinal  cord,  head  of,  82 
neck  of,  72 
Horns,  anterior,  of  spinal  cord,  72 
lateral,  of  spinal  cord,  72 
posterior,  of  spinal  cord,  72,  122 
Hypoglossal  nuclei,  connections  of,  152 

nucleus  of  Roller,  152 
Hypophysis  cerebri,  246,  276,  323 


Ideas,  center  for,  467 
Incisures  of  Lantermann,  35 

of  Schmidt,  35 
Infantile  spinal  paralysis,  501 
Inferior  cerebellar  arteries,  431 

frontal  artery,  422 
Infundibulum,  246,  279,  323 

development  of,  532 
Innervation,  fields  of,  45 
Insula,  310 
Intellectual    faculties,    higher,    centers  which 

preside  over,  480 
Interannular  segment,  34 
Interbrain,  244,  511 
Intercallatum,  263 


582 


INDEX. 


Intermediate  gray  suljstance,  74 
Internal  auditory  artery,  425 
capsule,  399,  407 

localization  of  lesions  of,  48S 
Internodal  segment,  34 
Interolivary  decussation,  144,  224 
Interparietal  fissure,  300,  546 
Interpeduncular  ganglion,  251,  258 

space,  323 
Intraparietal  fissure,  300,  546 
Intrinsic  cells  of  spinal  cord,  80 
Island  of  Reil,  310 
Iter  a  terlio  ad  quartum  ventricuium,  21 1 


J- 

Jugular  vein,  internal,  bulb  of,  445 


K. 

Karyochroine  nerve-cells,  22 
Karyoplasm,  17 
Keimzellen,  513 
Key,  131 

and  Retzius,  foramina  of,  285 
Krause,  end  bulbs  of,  40 

ventriculus  terminalis  of,  74 
Kronthal's  method    of    staining,  modification 

of,  565 
Kiiline,  fields  of  innervation  of,  45 


L. 

Labb6,  posterior  anastomotic  vein  of,  439 
Labia  cerebri,  393 
Lacunre  venosas  lateralis,  283,  442 
Lamina  medullaris  circumvoluta,  355 

involuta,  359 
Lamin?e  medullares,  252 
Lancisi,  nerves  of,  389 
Language,  centers  for,  465 
Lantermann,  incisures  of,  35 
Laryngeal  muscles,  center  for,  453 
Lateral  arteries  of  pons  and  medulla,  432,  434 

columns,  nuclei  of,  143 

fissure,  300 

limiting  layers,  90,  107 

nuclei,  143 

sinuses,  445 

ventricles,  393 
Leg-area  of  cerebral  cortex,  451,  452 
Lemniscus,  lateral,  1 81,  228 
mesial,  144,  223 
Lenticular  loop,  399,  402 

nucleus,  399 
Lenticulo-optic  arteries,  424 
Lenticulostriate  arteries,  424 
Lewis,  Bevan,  method  of  staining  of,  565 
Ligamentum  denticulatum,  66 
Ligula,  132 
Limbic  lobe,  317 
Lines  of  Frohmann,  ;^^ 
Lingual  gyrus,  300 
lobule,  316 


Lingula,  18S 
Lissauer,  column  of,  1 14 
Lissauer's  tract,  106 
Lobe,  falciform,  317 
frontal,  303 
limbic,  317 
occipital,  308 
olfactory,  327 

development  of,  550 
orbital,  305 
parietal,  306 
([uadrate,  306,  316 
slender,  193 
temporosphenoid,  313 
Lobule,  cuneate,  190 
diagastric,  190 
inferior  semilunar,  193 
lingual,  316 
paracentral,  305 
postcentral,  310 
precentral,  310 
Lobules  of  cerebrum,  303 

of  inferior  surface  of  cerebellar  hemi- 
sphere,  190 
of  superior  or  dorsal  surface  of  cere- 
Ijeliar  hemisphere,  190 
Lobus  centralis,  189 
gracilis,  193 
quadratus,  190 
Localization,  cerebral, 448 
Locomotor  ataxia,  502 
Locus  cceruleus,  243 

niger,  263,  325 
Long  arteries  of  brain,  416 
Longitudinal  sinus,  inferior,  443 
superior,  442 
Loop,  lenticular,  399,402 
Lumbar  enlargement  of  spinal  cord,  69 

region  of  spinal  cord,  II5 
Lays'  body,  259,  260 
Lymphatics  of  nervous  system,  58,  61 
Lymph-canals,  jjerivascular,  58 
Lymph-sjjace,  adventitial,  58,  63 
Lymph-spaces,  pericellular,  63 
Lyra,  414 

M. 

Magendie,  foramen  of,  132,  285 

Mallory,    method    of,    for    staining    neuroglia 

fibers,   569 
Mallory's    phosphotungstic-acid    hematoxylin 

for  staining  neuroglia,  57° 
Marchi  and  Lowenthal,  anterolateral  descend- 
ing tracts  of,  90    104,  204 
Marchi's  method  of  staining,  569 
Marginal  convolution,  315 
gyrus,  315 
sinus,  443 
Marginofrontal  artery,  421 
Martinotti,  cells  of,  349 

Median  arteries  of  pons  and  medulla,  432,  433 
Medulla,  anterior  columns  of,  126 
pyramids  of,  126 
lateral  areas  of,  126 

columns  of,  126 


INDEX. 


583 


Medulla,  median  septum  of,  146 
oblongata,  69,  125 

arterial  supply  to,  432 
development  of,  525 
lesions  of,  496 
posterior  area  of,  126 
raphe  of,  146 
spinalis,  64 
transverse  section  of,  at  level  of  first 

cervical  nerve,  137 
transverse    section    of,    at    level    of 

motor  crossway,  140 
transverse  section  of,  near  junction 
with  pons,  166 
Medullary  folds,  508 
groove,  508 
plate,  508 
ridges,  508 

velum,  inferior,  132,  194 
superior,  131,  194 
Medullated  nerve-fiber,  49 
nerve-fibers,  31 
Membrana  limitans  interna  of  retina,  263 
Membrane,  external  limiting,  of  retina,  264 
Membranes  of  brain,  280 
Meningeal  artery,  posterior,  425 
Menisques,  tactile,  42 
Mesencephalon,  210,  530 
Methylene-blue  method  of  staining,  Ehrlich's 

vital,  573 
Meynert's  bundle,  257 

commissure,  276 
Mid-brain,  530 

minute  anatomy  of,  212 
region  of,'2io 
Middle  cerebellar  arteries,  431 
cerebral  artery,  422 
zone  of  spinal  cord,  74 
Mind-blindness,  469 
Mitral  cells,  large,  of  olfactory  bulb,  330 

of  olfactory  bulb,  superficial  layer 
of  medium   and   small  -  sized, 

331 

Molecular  cortical  layer,  343 

layer  of  olfactory  bulb,  330 
of  retina,  external,  266 
inner,  265 
Monro,  foramen  of,  246 
Monticuluscerebelli,  189 
Motion,  cortical  area  governing,  449 
Motor  aphasia,  471 

area,  lesions  of  centrum  semiovale  be- 
neath, 485 
of  brain,  449 
cells  of  spinal  cord,  76 
convolutions,  307 
decussation,  140 
nerve-organs,  45 
nerve-plates,  45 
nerve-roots,  112 
nerves,  terminations  of,  45 
neurones,  peripheral,  76 
nucleus  of  vagus  and  glossopharyngeal 

nerve,  158 
oculi  nerve,  235 
speech-center,  471 


Motor  sprays,  45 

tract,  220,  408 

tracts,  376 
Mouth,  angle  of.  center  for  retraction  of,  453 
Miiller's  fluid,  562 
Multipolar  nerve-cells,  24 
Muscle-spindle,  43 
Muscular  atrophy,  progressive,  501 
Myelin,  34 

sheath,  Weigert's  method  of  staining, 

567 
Myelospongium,  514 


N. 

Naming  center,  468 
Nates,  211 
Nerve  cell-bodies,  47 
Nerve-cells,  arkyostichochrome,  21 
bipolar,  24 
cytochrome,  22 
forms  or  varieties  of,  24 
Golgi's  method  for  staining,  566 
granular,  24 
gyrochrome,  22 
histology  of,  17 
karyochrome,  22 
multipolar,  24 
of  Purkinje,  25 
of  spinal  cord,  76 
somatochrome,  18 
staining  of,   after  the  method   of 
Nissl,  564 
with  thionin,  564 
stichochrome,  21 
corpuscle,  17 
fiber,  medullated,  49 
fibers,  30,  31 

medullated,   31 
non-medullated,  31,  35 
olfactory,  layer  of,  320 
Remak's  35 
sympathetic,  35 
organs,  motor,  45 
plates,  motor,  45 
roots,  70 

anterior,  1 12 
motor,  112 
posterior,  113 
sensory,  113 
Nerves,  cranial,  development  of,  547 
motor,  terminations  of,  45 
of  Lancisi,  389 
olfactory,  326 

sensory,  terminations  of,  38 
spinal,  108 

terminations  of,  stains  for,  572 
Nerve-supply  of  cerebral  dura  mater,  2S4 
Nerve-terminations,  peripheral,  37 
Nerve-trees,  47 
Nerve-unit,  17,  47 
Nerve-vesicle,  17 
Nervi  nervorum,  37 
Nervous  process,  31 

system,  central,  embryology  of,  508 


5^4 


INDEX. 


Nervous  system,  difTerential  stains  for  various 

elements  of,  563 
Ner\'us  masticatorius,  184 
Neural  canal,  50S 
tube,  508 
Neuraxone,  31,  47»49 
Neurilemma,   35 
Neurocytes,  47 
Neurodendron,  47 
Neuroglia,  52 

cell*,  56 

fibers,  differential  stains  for,  569 
of  gray  matter  of  spinal  cord,  1 21 
of  spinal  cord,  117 
stains.  569 

subpial,  of  spinal  cord,  83 
Neurokeratin,  34 
Neurone,  17,  47 

motor,   51 
of  second  type,  52 
Neurones,  classification  of,  50 
long,  50 

motor,  peripheral,  76 
of  the  first  order,  76 
Neuroplasm,  ^^ 
Neurospongium,  514 
Neutral  carmin,  for  staining  axis-cylinders  and 

nerve-cells,  571 
Nidus  avis,  190 

Nigrosin  for  staining  axis-cylinders,  571 
Nissl  body,  18 

granules  of,  18 

method  of,  staining  of  nerve-cells  after, 
564 
Nodes,  Ranvier's,  34 
Nodulus,  189 

Non-medullated  nerve-fibers,  31,  35 
Nuclear  caps,  18 

layer  of  retina,  inner,  265 
outer,  266 
Nucleus  accessorius,  173 
ambiguus,  1 58 
amygdala,  407 
amygdaloid,  399 
arciformis,  163 
caudate,  399 
cuneatus,  13 1,  144 
embolliformis,  194 
for  the  back-muscles,  79 
globosus,  194 
gracilis,  131,  144 
hypothalamicus,  260 
lenticularis,  399 
magnocellularis  diflfusus,  I49 
pontis,  179 

reticularis  tegmenti,  146,  234 
sacral,  83 

subthalamicum,  260 
vestibularis,  174,  175 


O. 

Obex,  132 

Occipital  convolutions,  309 

cortex,  retinal  representation  in,  462 

fissure,  299 


Occipital  gyrus,  first,  309 

inferior,  309 
middle,  309 
second,  309 
superior,  309 
third,  309 
lobe,  308 

fissures  of,  546 

lesions    of  centrum    semiovale 
of,  48  7 
sinus,  443     . 

sulcus,  anterior  superior,  309 
inferior,  309 
lateral,  309 
vertical,  309 
Occipito-cerebellar  tract,  221 
Occipito-temporal  fissure,  547 

gyrus,  middle,  300 
Oculomotor  nucleus,  connections  of,  238 
Olfactory  bulb,  319,  328 

fourth  layer  of,  332 
large  mitral  cells  of,  330 
layer  of  central  nerve-fibers  of, 

332 
molecular  layer  of,  330 
outer  layer  of,  328 
pyramidal  cells  of,  330 
suptrficial     layer    of    medium 
and  small-sized   mitral   cells 

of.  33^ 
center,  483 

glomeruli,  layer  of,  329 
lobe,  327 

development  of,  550 
nerve-fibers,  layer  of,  328 
nerves,  326 
region,  326 

sphere  of  cerebral  cortex,  507 
sulcus,  306 
tract,  319,  332 

roots  of,  335 
Olivary  bodies,  126,  159 

accessory,  160 
superior,  176,  180 
body,  143 

connections  of   vestibular  nerve 

with,  177 
hilum  of,  160 
fasciculus,  105 
tract,  105 
Operculum,  anterior,  304 
Optic  chiasm,  274,  320 

development  of,  539 
cup,  552 
decussation,  520 
nerve-fibers  of  retina,  264 
ner\'es,  course  of,  268 

development  of,  552)  557 
recess,  246 
thalami,  248 

connection     of,    with    cerebral 
cortex,  251 
thalamus,  249 

anterior  nucleus  of,  252 
tubercle  of,  249 
connections  of,  258 


INDEX. 


^585 


Optic  thalamus,  development  of,  532 

lateral  nucleus  of,  249,  253 
median  nucleus  of,  253 
peduncles  of,  252 
posterior  nucleus  of,  253 
surfaces  of,  249 
ventral  nucleus  of,  253 
tract,  connections  of,  273 
tracts,  course  of,  268 
vesicle,  pedicle  of,  552 
stalk  of,  552 
Orbital  lobe,  305 
Orth's  fluid,  563 


Pacchionian  glands,  287 
Pacinian  corpuscles,  41 
Palsy,  Erb's,  500 
Paracentral  lobule,  305 
Paralysis,  acute  bulbar,  499 

Brown-Sequard's,  504 
crossed,  490 
infantile  spinal,  501 
spasmodic,  500 
Paraphasia,  486 
Paraplegia,  ataxic,  503 
Paraxones,  50 

Parietal  artery,  ascending,  422    . 
convolution,  inferior,  308 
superior,  307 
gyrus,  ascending,  306 
lobe,  306 

fissures  of,  546 

lesions  of  centrum  ovale  of,  486 
Parieto-occipital  fissure,  299 
Parietotemporal  artery,  423 
Pars  olfactoria,  337 
Pathetic  nerve,  240 
Pedicle  of  optic  vesicle,  552 
Peduncle,  inferior  cerebellar,  182 
Peduncles,  cerebellar,  202 

superior,  229 
cerebral,  220 
of  cerebellum,  188 
of  cerebrum,   325 
of  corpus  callosum,  388 
of  optic  thalamus,  252 
of  pineal  gland,  246 
Pedunculus  conarii,  247 
Pennicilli  olfactorii,  330 
Perforated  space,  posterior,  324 
spaces,  anterior,  320 
Pericellular  lymph-spaces,  63 
Perineurium,  36 

Peripheral  nerve  terminations,  37 
Perivascular  lymph  canals,  58 
Perpendicular  fasciculus,  370 
Pes  hippocampus,  394 

pedunculi,  220 
Petrosal  sinuses,  inferior,  445 

superior,  445 
Pia  mater,  65 

cerebral,  288 

nerves  of,  288 
Pigment-layer  of  retina,  267 


Pineal  gland,  246 

development  of,  532 
peduncles  of,  246 
posterior  commissure  of,  248 
Pitres'  method  of  sectioning  brain,  561 
Pituitary  body,  267,  276,  323 

development  of,  536 
Plate,  medullary,  508 
Plexuses,  choroid,  288,  289 
Poliomyelitis  anterior  acuta,  501 
Polygonal  cells,  254 
Polymorphous  cells,  layer  of,  350 
Pons,  development  of,  528 

transverse  section  of,  179 
Varolii,  178 

arterial  supply  to,  432 
lesions  of,  490 
Postcentral  lobule,  310 
sulcus,  300 
Posterior  cerebral  arteries,  425 

communicating  artery,  424 
meningeal  artery,  425 
Postparietal  gyrus,  308 
Precentral  fissure,  546 
lobule,  310 
sulcus,  304,  546 
Precuneus,  316 
Prepyramidal  fissure,  190 
Primary  fissure,  542 
Primitive  fibrillee,  ^^ 
sheath,  35 
Processus  ad  cerebrum,  188 
ad  medullam,  188 
ad  pontem,  188 
falciformis  major,  281 
minor,  282 
reticularis,  74 
Progression,  cross-legged,  500 
Progressive  muscular  atrophy,  501 
Projection  spheres  of  cerebral  cortex,  507 

system  of  fibers,  373 
Prosencephalon,  293,  511 
Protoplasmic  buds,  48 

granules,  18 
processes,  48 

of  Deiter,  47 
Psalterium,  373,  414 
Pulvinar,  249,  253 
Purkinje,  axis-cylinder  of,  32 
cells  of,  200 
nerve-cells,  25 
Putamen,  399 
Pyramid,  189 
Pyramidal  cells,  giant,  29 

large,  layer  of,  346 
of  cortex,  28 
of  olfactory  bulb,  330 
small,  layer  of,  345 
decussation,  140 

posterior,  144 
nuclei,  163 
tract,  220 
tracts,  anterior,  89 
crossed,  91 
direct,  89,  92 
Pyramids,  anterior,  140 


586 


IXDKX. 


rvianiids,  anterior,  of  medulla,  126 
posterior,  131 

Q- 

Quadrate  artery,  421 

lobe,  306,  316 


R. 

Radiation,  tegmental,  403 
Ranvier,  tactile  menisques  of,  42 
Ranvier's  nodes,  34 
Raphe,  527 

of  medulla,  146 
Rautenlippe,  526 
Recess,  optic,  246 
Red  nucleus,  259,  261 

connections  of,  262 
Regio  olfactoria,  326 
Reil,  fasciculus  uncinatus  of,  368 
island  of,  310 

fissures  of,  546 
sulci  of,  546 
Remak's  nerve-fibers,  35 
Restiform  bodies,  131,  164 
Retina,  263 

development  of,  552,  556 

external  limiting  memljrane  of,  264 

molecular  layer  of,  266 
ganglionic  cells  of,  264 
inner  molecular  layer  of,  265 

nuclear  layer  of,  265 
membrana  limitans  interna  of,  263 
optic  nerve- fibers  of,  264 
outer  nuclear  layer  of,  266 
pigment  layer  of,  267 
rods  and  cones  of,  266,  557 
Retinal  representation  in  the  occipital  cortex, 

462 
Ridges,  medullary,  50S 
Rindenschicht,  119 
Rods  and  cones  of  retina,  266,  557 
Rolando,  fissure  of,  299,  545 

substantia  gelatinosa  of,  73 
tubercle  of,  137 
Roller,  hypoglossal  nucleus  of,  152 
Roof  nucleus  of  Stilling,  194 
Root  arteries,  123 

anterior,  1 23 

of  pons  and  medulla,  432,  434 
posterior,  123 
zone,  posterior,  of  spinal  cord,  84,  91 
Roots,  anterior,  of  spinal  nerves,  108 
posterior,  of  spinal  nerves,  108 
Rostrum,  414 


Sacral  nucleus,  83 

Sagittal  sinus,  442 

Schmidt,  incisures  of,  35 

Schultze,   comma-shaped  bundle  of,  99 

Schwann,  white  substance  of,  34 

Sclerosis,  amyotrophic  lateral,  501 


Sclerosis,  primary  lateral,  500 
Secondary  degeneration,  87 
Segment,  iiiteraniiular,  34 

internodal,  34 
Semilunar  lobe,  posterior  superior,  190 

lobule,  inferior,   193 
Sensations,  general,  cortical  center  for,  454 
Sensory  center  for  writing,  479 

cerebellar  tract,  direct,  166,  177,  207 

cranial  nerves,  ganglia  of,  548 

decussation,  144 

fibers  of  cranial  nerves,  547 

nerve-roots,  1 13 

nerves,  terminations  of,  38 

spheres  of  cerebral  cortex,  507 

tract,  382,  408 

long,  in  gray  matter,  106 
tracts  of  the  spinal  cord,  95 
Septomarginal  descending  tract,  loo,  102 
Septum,  intermediate,  91 
luciduni,  414 

vein  of,  440 
median,  of  medulla,  146 
postero-intermediate,  126 
ventral,  of  spinal  cord,  71 
Sheath,  primitive,  35 

tubular,  35 
Sinus,  basilar,  444 
circular,  444 
confiuens,  442 
falciform,  442 
inferior,  longitudinal,  443 
jugularis,  445 
marginal,  443 
occipital,  443 
sagittal,  442 
sphenoparietal,  446 
straight,  443 
superior  longitudinal,  442 
transverse,  444 
Sinuses,  cavernous,  446 

inferior  petrosal,  445 
lateral,  445 
superior  petrosal,  445 
venous,  442 
Sixth  nerve,  nuclei  of,  connections  of  vestii>ular 

nerve  with,  177 
Slender  lobe,  193 

Slit,  anterolateral,  of  spinal  cord,  72 
Smell,  cortical  center  for,  483 
Somatochrome  nerve-cells,  18 
Space,  interpeduncular,  323 
of  Broca,  335 
posterior  perforated,  324 
Virchow-Robin,  58 
Spaces,  anterior  perforated,  320 

subarachnoid,  285 
Spasmodic  paralysis,  500 
Speech-center,  motor,  471 
Sphenoid  artery,  423 
Sphenoparietal  sinus,  446 
Spider-cells  of  Deiter,  56 
Spinal  accessor}-  nerve,  139 
arteries,  anterior,  122 
lateral,  123 
posterior,  122 


INDEX. 


587 


Spinal  cord,  64 

accessory  nucleus  of,  76 
anterior  column  of,  84 

commissure  of,  74 

cornua  of,  72 

horns  of,  72 

longitudinal  fissure  of,  71 
anterolateral  mixed  zone  of,  90 

slit  of,  72 
blood-supply  of,  122 
central  canal  of,  74,  122 
cervical  enlargement  of,  69 

region  of,  117 
commissural  cells  of,  83 
commissures  of,  71 
complete    transverse    lesions    of, 

504 

cornua  of,  72 

development  of,  513 

dorsal  enlargement  of,  69 
fissure  of.  71,  72 
region  of,  116 

extent  of,  66 

gray  matter  of,  7 1 

head  of,  horns  of,  72 

intrinsic  cells  of,  80 

lateral  columns  of,  84 
horns  of,  72 

lesions,  localization  of,  499 

lumbar  enlargement  of,  69 
region  of,  1 15 

middle  zone  of,  74 

motor  cells  of,  76 

neck  of,  horns  of,  72 

nerve-ceils  of,   76 

neuroglia  of,  117 

posterior  columns  of,  84 

commissure  of,  74,  75 
fissui-e  of,  72 
horns  of,  72,  122 
longitudinal  fissure    of, 

71 

root- zone  of,  84,  9 1 
postero-intermediate    fissure    of, 

72 
postero-internal  column  of,  91 
posterolateral  groove  of,  72 
removal  of,  563 
sensory  tracts  of,  95 
subpial  neuroglia  of,  83 
technic  of  macroscopic  and  micro- 
scopic examination  of,  559 
thoracic  region  of,  1 16 
transverse  section  of,  at  different 

levels,  114 
veins  of,  124 
ventral  fissure  of,  71 

septum  of,  71 
white  commissure  of,  74 
matter  of,  71,  83 
ganglia,  109 

posterior,  function  of,  112 
ganglion,  posterior,  71 
nerves-,  108 

posterior  roots  of,  108 
Spitzka,  intercallatum  of,  263 


Spongioblasts,  265,  514 
Sprays,  motor,  45 

Stains,    differential,    for   various    elements   of 
nervous  system,  573 
for  axis-cylinder  processes,  571 
for  collateral  branches,  572 
for  end  organs,  512 
for  terminations  of  nerves,  572 
general,  573 
neuroglia,  569 
Stalk  of  optic  vesicle,  552 
Stellate  cells,  56,  254 
Stichochrome  nerve-cells,  21 
Stilling,  red  nucleus  of,  261 
roof  nucleus  of,  194 
sacral  nucleus  of,  83 
substantia  gelatinosa  centralis  of,  74 
tegmental  nucleus  of,  261 
Strahlenzellen,  254 
Straight  sinus,  443 
Stratum  gelatinosum,  330 
glomerulorum,  329 
granulosum,  360 
intermedium,  259 
lacunosum,  355,  356,  357,  359 
moleculare,  355,  359 
oriens,  354,   356 
radiatum,  357 
zonale,  248,  324,  355,  359 

of  cerebral  cortex,  338 
Stria  terminalis,  249,  404 
StricC  acusticse,  135^ 

cornese,  398,  404 
Subarachnoid  space,  65 

spaces,  285 
Subiculum  cornu  ammonis,  317,  350 
Subpial  neuroglia  layer,  119 

of  spinal  cord,  83 
Substantia  ferruginea,  182 

gelatinosa  centralis,  74 

of  Rolando,  73 
Rolandi,  122 
nigra,  220,  259,  263,  325 
reticularis  alba,  355 
Subthalamic  region,  259 
Sulci,  294 

of  island  of  Reil,  546 
Sulcus,  anterior  superior  occipital,  309 
centralis  insuke,  310 
choroideus,  249 
inferior  occipital,  309 
lateral  occipital,  309 
lateralis,  220 
limitans  insula,  310 
oculomotorius,  220,  237 
olfactory,  306 
postcentral,  300 
precentral,  304,  546 
vertical  occipital,  309 
Superior  cerebellar  arteries,  430 
Supramarginal  gj'rus,  308 
Sylvian  aqueduct,  132 
artery,  422 
fissure,  320 
Sylvius,  aqueduct  of,  210 

development  of,  530 


sss 


INDEX. 


Sylvius,  fissure  of,  298 

development  of,  540 
fossa  of,  development  of,  540 
Sympathetic  nerve- fibers,  35 
Syringomyelia,  503 


Tactile  aphasia,  471 
corpuscles,  39 
menisques,  42 
Taenia  cornu,  249 

semicircularis,  249,  398,  404 
Tangential  fibers  of  cerebral  cortex,  339 
Tapetum,  390 

Taste,  cortical  centers  for,  482 
Tegmental  nucleus,  194,  261 
radiation,  403 
tract,  central,   163 
Tegmentum,  220,  223,  325 
Tela  choroidea  inferior,  2S5,  291 
Telodendrons,  47,  50 
Temporal  convolution,  first,  313 

inferior,  314 
middle,  314 
second,  314 
superior,   313 
third,  314 
lobe,  fissures  of,  546 

lesions  of  centrum  semiovale, 
486 
Temporocerebellar  tract,  221 
Temporoparietal  convolutions,  310 
Temporosphenoid  lobe,  313 
Tenia,  132 

Tentorium  cerebelli,  186,  281 
Testes,   211 

Thalamencephalon,   244,511 
Thionin,  staining  of  nerve-cells  with,  564 
Third  pair  of  cranial  nerves,  235 
Thoracic  region  of  spinal  cord,  n6 
Tonsil,  190 

TorcuJar  Herophili,  442 
Tract,  acousticocerebellar,  166,  177,  207 

anterolateral  ascending,  80,  193,  233 

function  of,  104 
descending  cerebellar,  104 
central  tegmental,  163 
cerebello-olivary,    160,  164,  207 
connecting  occipital  and  temporal  lobes 

with  cerebellar  hemispheres,  221 
cornu  commissural,  100,  loi 
descending  cerebellar,  204 
direct  cerebellar,  83,  95 
pyramidal,  92 

sensor}'  cerebellar,  166,  177 
frontocerebellar,  222,  375 
Gowers',  385 
Lissauer's,  106 

long  sensory,  in  gray  matter,  106 
motor,  loS,  220 
occipitocerebellar,  221 
olfactor}-,  319 

roots  of,  335 
olivary,  105 


Tract,  pyramidal,   220 
sensory,  382,  408 

septomarginal,  descending,    loo,  102 
temporocerebellar,  221 
uncrossed  pyramidal,  92 
Tracts,  anterior  pyramidal,  89 

anterolateral  ascending,  of  Gowers,  90 

descending,  90 
crossed  motor,  90 

pyramidal,  90,  9I 
direct  cereljeliar,  90,  143,  203 
pyramidal,  89,  91 
sensory  cerebellar,  207 
motor,  376 
olfactory,  332 

sensor}\  of  the  spinal  cord,  95 
Tractus  striothalamicus,  403 
Transverse  sinus,  444 
Triangular  bundle,  105 
Trigeminal  nerve,  accessory  nucleus  of,  240 

cerel)ral  connections  of,  185 
motor  root  of,  182,  184 
nuclei  of  origin  of,  182 
sensory  root  of,  182 
Trigonum  habenulce,  249 

olfaciorium,  335 
ventriculi,  394 
Trochlear  nerve,  240 
Trolard,  great  anastomotic  vein  of,  439 
Trunk  and  spine,  muscles  of,  cortical  area  for, 

453 
Tul)e,  neural,  508 
Tuber  cinereum,  279,  323 

valvulce,  190 
Tubercle,  399 

anterior,  of  optic  thalamus,  249 
of  Rolando,  131,  137 
Tuberculum  acusticum,  173,  174 
anterius,  252 
nervi  facialis,  168 
Tubular  sheath,  35 
Tunica  adventitia  of  arteries,  58 
intima  of  arteries,  59 
media  of  arteries,  59 
Tiirck,  columns  of,  89 
Twelfth  pair  of  cranial  nerves,  nuclei  of,  151 


U. 

Uncinate  gyrus,  318 

Uncus,  318 

Upper  extremity,  cell-group  for,  79 

Uvula,  1 89 


Vagus,  155 

motor  nucleus  of,   158 
Vallecula,  186 

Sylvii,  298 
Valve  of  Vieussens,  132,  194 
Van  Gieson's  method  of  staining,  571 
Vater's  corpuscles,  41 
Vein,  anterior  cerebral,  437 
basilar,  437 


INDEX. 


589 


Vein,  choroid,  440 
falciform,  443 
great  anastomotic,  439 
middle  cerebral,  437 
of  corpus  striatum,  440 
of  septum  lucidum,  440 
posterior  anastomotic,  439 
Veins,  cerebral,  435 

deep  cerebral,  440 
emissary,  447 
inferior  cerebellar,  441 
of  cerebellum,  440 
of  convolutions,  438 
of  Galen,  440 
of  nervous  system,  60 
of  spinal  cord,  124 
superficial  cerebral,  436 
superior  cerebellar,  440 
Velum  interpositum,  288 

medullary,  inferior,  132, '194 
superior,  1 31,  194 
Venous  sinuses,  442 

systems  of  brain,  435 
Ventral  septum  of  spinal  cord,  71 
Ventricle,  fifth,  414 
fourth,  131 

choroid  plexuses  of,  291 
of  Arantius,   125,  136 
of  corpus  callosum,  393 
third,  middle  commissure  of,  245 
region  of,  244 
soft  commissure  of,  245 
Ventricles,  lateral,  393 

cornua  of,  393 
Ventriculus  terminalis,  74 
Verbal  aphasia,  468 
Vermiform  process  of  cerebellum,  186 

inferior,  186 
Vermis,  186,   187,  188 

inferior  surface  of,  189 
superior  surface  of,  188 
Vertebral  arteries,  425 
Vesicle,  second  primitive,  530 

third  cerebral,  530 
Vesicles,  primary  cerebral,  508 

secondary  cerebral,  511 
Vesicular  column,  83 
Vestibular  nerve,  171,  172 


Vestibular  nerve,  connections  of,  176 

of,  with  cerebel- 
lum, 176 
of,  with  internal 
or  mesial  fillet, 
177 
of,    with    lateral 

column,  177 
of,    with    lateral 

fillet,  177 
of,    with    nuclei 
of  sixth  nerve, 
177 
of,   with    olivary 
body, 177 
Vicq  d' Azyr,  bundle  of,  253,  324,  413 

white  layer  of,  339 
Vieussens,  valve  of,  132,  194 
Villi,  arachnoid,  287 
Virchow-Robin  space,  58 
Virchow's  method  of  sectioning  brain,  560 
Vision,  centers  of,  457 
Visual  sphere  of  cerebral  cortex,  507 


W. 

Wedge,  131 

Weigert's    method    of    staining    the    myelin 

sheath,  567 
Wernicke,  perpendicular  fasciculus  of,  370 
White  matter  of  spinal  cord,  71,  83 

substance  of  Schwann,  34 
Wilder,  occipital  fissure  of,  299 
Willis,  circle  of,  429 
Word-blindness,  470 
Worm  of  cerebellum,  186,  188 

superior,  187 
Wrisberg,  nerve  of,  168 
Writing,  cortical  center  for,  475 
sensory  center  for,  479 


Z. 

Zona  incerta,  259 

Zone,  anterolateral  mixed,  of  spinal  cord,  90 

middle,  of  spinal  cord,  74 
Zones  of  association  of  cerebral  cortex,  507 


